US20030160538A1 - Semiconductor device - Google Patents

Abstract

A flexible area2is joined at one end via a thermal insulation area7to a semiconductor substrate3which becomes a frame and at an opposite end to a moving element5.The thermal insulation area7is made of a thermal insulation material a resin such as polyimide or a fluoridated resin. The flexible area2is made up of a thin portion2S and a thin film2M different in thermal expansion coefficient. When a diffused resistor6formed on the surface of the thin portion2S is heated, the flexible area2is displaced because of the thermal expansion difference between the thin portion2S and the thin film2M, and the moving element5is displayed with respect to the semiconductor substrate3.

Description

BACKGROUND OF INVENTION
• 1. Field of Invention[0001]
• This invention relates to a semiconductor device made up of a semiconductor substrate, a flexible area isolated from the semiconductor substrate and displaced in response to temperature change, and a heat insulation area placed between the semiconductor substrate and the flexible area, a semiconductor microactuator using the semiconductor device, a semiconductor microvalve, a semiconductor microrelay, and a semiconductor microactuator manufacturing method.[0002]
• 2. Related Art[0003]
• A semiconductor microactuator includes at least two materials having different thermal expansion coefficients in combination as a bimetal structure wherein the bimetal structure is heated and the difference between the thermal expansion coefficients is used to provide displacement is available as a mechanism using a semiconductor device made up of a semiconductor substrate, a flexible area isolated from the semiconductor substrate and displaced in response to temperature change, and a heat insulation area placed between the semiconductor substrate and the flexible area. The semiconductor microactuator is disclosed in U.S. Pat. No. 5,069,419 “Semiconductor microactuator.”[0004]
• A semiconductor microactuator described in U.S. Pat. No. 5,069,419 is as shown in FIG. 53 (top view) and FIG. 54 (sectional view); it has a flexible area of a bimetal structure comprising an aluminum[0005]thin film304 formed in a part of asilicon diaphragm300. If an electric current is made to flow into aheater301 formed in thesilicon diaphragm300, heat is generated and the temperature of thediaphragm300 rises. Since silicon and aluminum differ largely in thermal expansion coefficient, a thermal stress occurs, bending thediaphragm300, producing displacement of a moving part305 placed contiguous with thediaphragm300. To provide efficient displacement, ahinge303 of a silicon dioxide thin film is placed between the periphery of thediaphragm300 and asilicon frame302 of a semiconductor substrate for preventing heat generated in thediaphragm300 from escaping to thesilicon frame302.
• However, considering the current state of application, it is desired to furthermore decrease the heat loss. Specifically, the heat escape (heat loss) is thought of as power (consumption power) supplied all the time to maintain the[0006]diaphragm300 at a predetermined temperature (for example, 150° C.).
• Then, it is desired that the power consumption is 100 mW or less considering miniature, portable battery-driven applications.[0007]
• Further, as examples of semiconductor microrelays in related arts, semiconductor microrelays are disclosed in JP-A-6-338244 and JP-A-7-14483. The semiconductor microrelays disclosed therein will be discussed with reference to the accompanying drawing.[0008]
• FIG. 55 is a sectional view to show the structure of the semiconductor microrelay in the related art. As shown in FIG. 55, the semiconductor microrelay has a[0009]cantilever beam313 having a first thermal expansion coefficient and made of asilicon monocrystalline substrate312 with an opposite end supported so that one end can be moved. On the rear side of thecantilever beam313, the semiconductor microrelay has ametal layer315 having a second thermal expansion coefficient larger than the first thermal expansion coefficient via aconductive layer315. On the main surface of thecantilever beam313, acontact circuit317 is provided via anoxide film314 on the one end side. Also, aheater circuit318 is provided via theoxide film314 on the roughly full face of the main surface of thecantilever beam313.
• On the other hand, an[0010]opposed contact part320 having aconductive layer319 as an opposed surface is provided at a position facing thecontract circuit317 with a predetermined space above thecontract circuit317. An electric current is made to flow into theheater circuit318, whereby theheater circuit318 is heated. Thus, a flexible area consisting of thecantilever beam313 and themetal layer316 is heated. At this time, the thermal expansion coefficient of themetal layer316 is set larger than that of thecantilever beam313, so that thecantilever beam313 and themetal layer316 are displaced upward. Therefore, thecontact circuit317 provided on the one end of thecantilever beam313 is pressed against theopposed contact part320 and is brought into conduction. Such a bimetal-driven relay enables an increase in the contact spacing and an increase in the contact load as compared with a conventional electrostatically driven relay. Thus, a relay with small contact resistance and good reliability with less welds, etc., can be provided.
• However, the semiconductor microrelay in the related art also involves the following problem: To drive the relay, it is necessary to make an electric current flow into the[0011]heater circuit318 provided on the main surface of thecantilever beam313 for heating thecantilever beam313 and themetal layer316. However, the silicon monocrystal forming thecantilever beam313 is a material having very good thermal conductivity, thecantilever beam313 is connected at the opposite end to thesilicon monocrystalline substrate312, and large heat is escaped from thecantilever beam313 to thesilicon monocrystalline substrate312, so that it becomes extremely difficult to raise the temperature of thecantilever beam313 with small power consumption.
• That is, with the semiconductor microrelay in the related art, large power must be supplied all the time to maintain the conduction state. The value is extremely large as compared with a mechanical relay that can be driven with several ten mW. For practical use, realizing low power consumption is a large challenge.[0012]
SUMMARY OF INVENTION
• As described above, the semiconductor microactuator using the semiconductor device, the semiconductor microvalve, and the semiconductor microrelay in the related arts require large power consumption and thus it becomes difficult to drive them with a battery and it is made impossible to miniaturize them for portable use.[0013]
• It is therefore an object of the invention to provide a semiconductor device with small power consumption, manufactured by an easy manufacturing process, a semiconductor microactuator using the semiconductor device, a semiconductor microvalve, a semiconductor microrelay, and a semiconductor microactuator manufacturing method.[0014]
• To the end, according to a first aspect of the present invention, there is provided a semiconductor device comprising a semiconductor substrate, a flexible area being isolated from the semiconductor substrate and displaced in response to temperature change, and a thermal insulation area being placed between the semiconductor substrate and the flexible area and made of a resin for joining the semiconductor substrate and the flexible area. The thermal insulation area made of a resin is placed between the semiconductor substrate and the flexible area, whereby heat escape when the temperature of the flexible area is changed is prevented, so that power consumption can be suppressed and further the manufacturing method is simple.[0015]
• In a second aspect to the present invention, in the semiconductor device as first aspect of the present invention, the material of which the thermal insulation area is made has a thermal conductivity coefficient of about 0.4 W/(m ° C.) or less. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced.[0016]
• In a third aspect of the present invention, in the semiconductor device as the second aspect of the present invention, the material of which the thermal insulation area is made is polyimide. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced and manufacturing the semiconductor device is facilitated.[0017]
• In a fourth aspect of the present invention, in the third aspect of the present invention, the material of which the thermal insulation area is made is a fluoridated resin. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced and manufacturing the semiconductor device is facilitated.[0018]
• In a fifth aspect of the present invention, in the first to fourth aspect of the present invention, a reinforcement layer made of a harder material than the material of which the thermal insulation area is made is provided on at least one face orthogonal to a thickness direction of the thermal insulation area. The joint strength of the semiconductor substrate and the flexible area can be increased.[0019]
• In a sixth aspect of the present invention, in the fifth aspect of the present invention, the reinforcement layer has a Young's modulus of 9.8×10[0020]⁹N/m²or more. The joint strength of the semiconductor substrate and the flexible area can be increased.
• In a seventh aspect of the present invention, in the sixth aspect of the present invention, the reinforcement layer is a silicon dioxide thin film. The joint strength of the semiconductor substrate and the flexible area can be increased.[0021]
• In an eighth aspect of the present invention, in the first to seventh aspect of the present invention, the portions of the semiconductor substrate and the flexible area in contact with the thermal insulation area form comb teeth. The joint strength of the semiconductor substrate and the flexible area can be increased.[0022]
• According to a ninth aspect of the present invention, there is provided a semiconductor device comprising a semiconductor device as the first to eighth aspect of the present invention and a moving element placed contiguous with the flexible area, wherein when temperature of the flexible area changes, the moving element is displaced relative to the semiconductor substrate. The semiconductor device which has similar advantages to those in the invention as claimed in[0023]claims 1 to 8 as well as can be driven with low power consumption can be provided.
• In a tenth aspect of the present invention, in the ninth aspect of the present invention, the flexible area has a cantilever structure. The semiconductor device can be provided with large displacement of the moving element.[0024]
• In an eleventh aspect of the present invention, in ninth aspect of the present invention, the moving element is supported by a plurality of flexible areas. The moving element can be supported stably.[0025]
• In a twelfth aspect of the present invention, in the eleventh aspect of the present invention, the flexible areas are in the shape of a cross with the moving element at the center. Good displacement accuracy of the moving element can be provided.[0026]
• In a thirteenth aspect of the present invention, in the ninth aspect of the present invention, displacement of the moving element contains displacement rotating in a horizontal direction to a substrate face of the semiconductor substrate. The displacement of the moving element becomes large.[0027]
• In a fourteenth aspect of the present invention, in the eleventh or thirteenth aspect of the present invention, the flexible areas are four flexible areas each shaped like L, the four flexible areas being placed at equal intervals in every direction with the moving element at the center. The lengths of the flexible areas can be increased, so that the displacement of the moving element can be made large.[0028]
• In a fifteenth aspect of the present invention, in the ninth to fourteenth aspect of the present invention, the flexible area is made up of at least two areas having different thermal expansion coefficients and is displaced in response to the difference between the thermal expansion coefficients. As the temperature of the flexible area is changed, the flexible area can be displaced.[0029]
• In a sixteenth aspect of the present invention, in the fifteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of aluminum. As the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between aluminum and silicon.[0030]
• In a seventeenth aspect of the present invention, in the fifteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of nickel. As the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between nickel and silicon.[0031]
• In a eighteenth aspect of the present invention, in the fifteenth aspect of the present invention, at least one of the areas making up the flexible area is made of the same material as the thermal insulation area. Since the flexible area and the thermal insulation area can be formed at the same time, the manufacturing process is simplified and the costs can be reduced.[0032]
• In a nineteenth aspect of the present invention, in the eighteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of polyimide as the area made of the same material as the thermal insulation area. In addition to a similar advantage to that in the invention, as the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between silicon and polyimide, and the heat insulation properties of the flexible area owing to polyimide.[0033]
• In a twentieth aspect of the present invention the invention, in the eighteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of a fluoridated resin as the area made of the same material as the thermal insulation area. In addition to a similar advantage, as the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between silicon and the fluoridated resin, and the heat insulation properties of the flexible area owing to the fluoridated resin.[0034]
• In a twenty-first aspect of the present invention, in the ninth to fourteenth aspect of the present invention, the flexible area is made of a shape memory alloy. As the temperature of the flexible area is changed, the flexible area can be displaced.[0035]
• In a twenty-second aspect of the present invention, in the ninth to twenty-first aspect of the present invention, a thermal insulation area made of a resin for joining the flexible area and the moving element is provided between the flexible area and the moving element. The heat insulation properties between the flexible area and the moving element can be provided and power consumption when the temperature of the flexible area is changed can be more suppressed.[0036]
• In a twenty-third aspect of the present invention, in the twenty-second aspect of the present invention, wherein rigidity of the thermal insulation area provided between the semiconductor substrate and the flexible area is made different from that of the thermal insulation area provided between the flexible area and the moving element. The displacement direction of the moving element can be determined depending on the rigidity difference between the thermal insulation areas.[0037]
• In a twenty-fourth aspect of the present invention, in the ninth to twenty-third aspects of the present invention, the flexible area contains heat means for heating the flexible area. The semiconductor device can be miniaturized.[0038]
• In a twenty-fifth aspect of the present invention, in the ninth to twenty-fifth aspects of the present invention, wiring for supplying power to the heat means for heating the flexible area is formed without the intervention of the thermal insulation area. The heat insulation distance of the wiring can be increased and the heat insulation properties of the flexible area can be enhanced.[0039]
• In a twenty-sixth aspect of the present invention, in the ninth to twenty-fifth aspect of the present invention, the moving element is formed with a concave part. The heat capacity of the moving element is lessened, so that the temperature change of the flexible area can be accelerated.[0040]
• In a twenty-seventh aspect of the present invention, in the ninth to twenty-sixth aspects of the present invention, a round for easing a stress is provided in the proximity of the joint part of the flexible area and the moving element or the semiconductor substrate. The stress applied in the proximity of the joint part when the flexible area is displaced is spread by means of the round, whereby the part can be prevented from being destroyed.[0041]
• In a twenty-eighth aspect of the present invention, in the twenty-seventh aspect of the present invention, the semiconductor substrate is formed with a projection part projecting toward the joint part to the flexible area and the round is formed so that the shape of the round on the substrate face on the semiconductor substrate becomes like R at both ends of the base end part of the projection part. The stress applied to both ends of the base end part of the projection part when the flexible area is displaced is spread by means of the round, whereby the portion can be prevented from being destroyed.[0042]
• In a twenty-ninth aspect of the present invention, in twenty-seventh aspect of the present invention, the semiconductor substrate is etched from the substrate face to make a concave part, the flexible area is formed in a bottom face part of the concave part, and the round is formed so as to become shaped like R on the boundary between the bottom face part and a flank part of the concave part. The stress applied to the boundary between the bottom face part and the flank part of the concave part when the flexible area is displaced is spread by means of the round, whereby the portion can be prevented from being destroyed.[0043]
• According to a thirtieth aspect of the present invention, there is provided a semiconductor microvalve comprising a semiconductor device in any of ninth to twenty-ninth aspects and a fluid element being joined to the semiconductor device and having a flow passage with a flowing fluid quantity changing in response to displacement of the moving element. The semiconductor microvalve which has similar advantages in ninth to twenty-ninth aspect of the present invention as well as can be driven with low power consumption can be provided.[0044]
• In a thirty-first aspect of the present invention, in the thirties of the present invention, the semiconductor device and the fluid element are joined by anodic junction. It is made possible to join the semiconductor device and the fluid element.[0045]
• In a thirty-second aspect of the present invention, in the thirties aspect of the present invention, the semiconductor device and the fluid element are joined by eutectic junction. It is made possible to join the semiconductor device and the fluid element.[0046]
• In a thirty-third aspect of the present invention, in the thirtieth aspect of the present invention, the semiconductor device and the fluid element are joined via a spacer layer. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed in the spacer layer and the stress applied to the flexible area can be suppressed.[0047]
• In a thirty-fourth aspect of the present invention, in the thirty-third aspect of the present invention, the spacer layer is made of polyimide. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed because of elasticity of polyimide and the stress applied to the flexible area can be suppressed.[0048]
• According to a thirty-fifth aspect of the present invention, there is provided a semiconductor microrelay comprising a semiconductor device as the ninth to twenty ninth aspect of the present invention and a fixed element being joined to the semiconductor device and having fixed contacts being placed at positions corresponding to a moving contact provided on the moving element, the fixed contacts being able to come in contact with the moving contact. The semiconductor microrelay which has similar advantages to those in the invention as claimed in claims 9 to 29 as well as can be driven with low power consumption can be provided.[0049]
• In a thirty-sixth aspect of the present invention, in the thirty-fifth aspect of the present invention, the fixed contacts are placed away from each other and come in contact with the moving contact, whereby they are brought into conduction via the moving contact. The semiconductor microrelay wherein the fixed contacts placed away from each other can be brought into conduction can be provided.[0050]
• In a thirty-seventh aspect of the present invention, in the thirty-fifth or thirty-sixth aspect of the present invention, the moving contact and the fixed contacts are gold cobalt. The moving contact and the fixed contacts can be brought into conduction.[0051]
• In a thirty-eighth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined by anodic junction. It is made possible to join the semiconductor device and the fixed element.[0052]
• In a thirty-ninth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined by eutectic junction. It is made possible to join the semiconductor device and the fixed element.[0053]
• In a fortieth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined via a spacer layer. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed in the spacer layer and the stress applied to the flexible area can be suppressed.[0054]
• In a forty-first aspect of the present invention, in the fortieth aspect of the present invention, the spacer layer is made of polyimide. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed because of elasticity of polyimide and the stress applied to the flexible area can be suppressed.[0055]
• According to a forty-second aspect of the present invention, there is provided a manufacturing method of a semiconductor device in the eighteenth aspect of the present invention prepared by a process comprising the steps of:[0056]
• etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;[0057]
• etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;[0058]
• etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0059]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0060]
• applying a coat of the thermal insulation material to the one face of the semiconductor substrate to form one area forming a part of the flexible area.[0061]
• The thermal insulation area and one area forming a part of the flexible area are formed of the same material at the same time, whereby the manufacturing process is simplified and the costs can be reduced.[0062]
• According to a forty-third aspect of the present invention, there is provided a manufacturing method of a semiconductor device in sixteenth aspect of the present invention prepared by a process comprising the steps of:[0063]
• etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;[0064]
• etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;[0065]
• etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0066]
• forming an aluminum thin film as an area defined in the flexible area on the other face of the semiconductor substrate and a wire for applying an electric power to the heating means;[0067]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area.[0068]
• whereby the manufacturing process is simplified and the costs can be reduced.[0069]
• According to a forty-fourth aspect of the present invention, there is provided a manufacturing method of a semiconductor device in seventeenth aspect of the present invention prepared by a process comprising the steps of:[0070]
• etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;[0071]
• etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;[0072]
• etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0073]
• forming a wire for applying an electric power to the heating means;[0074]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0075]
• forming a nickel thin film as an area defined in the flexible area on the other face of the semiconductor substrate.[0076]
• According to a forty-fifth aspect of the present invention there is provided a manufacturing method of a semiconductor device in the first aspect of the present invention prepared by a process comprising the steps of:[0077]
• etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0078]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0079]
• etching and removing the other face of the semiconductor substrate to form the thermal insulation area.[0080]
• According to a forty-sixth aspect of the present invention, there is provided a manufacturing method of a semiconductor device in the fifth aspect of the present invention prepared by a process comprising the steps of:[0081]
• etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0082]
• forming a reinforce layer in the thermal insulation area;[0083]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0084]
• etching and removing the other face of the semiconductor substrate to form the thermal insulation area.[0085]
• This invention is carried out paying attention to the fact that a resin material such as polyimide or a fluoridated resin has high heat insulation properties (about 80 times those of silicon dioxide) and further is liquid and easy to work and that a thin film having any desired thickness (several μm to several ten μm) can be easily provided by a semiconductor manufacturing process of spin coat, etc.[0086]
BRIEF DESCRIPTION OF THE DRAWINGS
• In the accompanying drawings:[0087]
• FIG. 1 is a partially cutaway view in perspective of the structure of a semiconductor microactuator using a semiconductor device corresponding to a first embodiment of the invention;[0088]
• FIG. 2([0089]a) is a sectional view to show the structure of the semiconductor microactuator in FIG. 1 and FIG. 2(b) is a top view to show the structure of the semiconductor microactuator in FIG. 1;
• FIG. 3 is a sectional view to show the structure of the semiconductor device in FIG. 1;[0090]
• FIGS.[0091]4(a) to4(c) show a structure model used to find the strength of the semiconductor device in FIG. 1; FIG. 4(a) is a schematic drawing, FIG. 4(b) is a distribution drawing, and FIG. 4(c) is a distribution drawing;
• FIGS.[0092]5(a) to5(d) are sectional views to show a manufacturing method of the semiconductor device in FIG. 1;
• FIGS.[0093]6(a) and6(b) are a sectional view and a top view to show the structure of another semiconductor device;
• FIG. 7 is a sectional view taken on line Y-Y′ in FIG. 6([0094]b) to show the structure of the semiconductor device in FIGS.6(a) and6(b);
• FIGS.[0095]8(a) to8(e) are sectional views to show a manufacturing method of the semiconductor device in FIGS.6(a) and6(b);
• FIGS.[0096]9(a) and9(b) are a sectional view and a top view to show the structure of still another semiconductor device;
• FIG. 10 is a sectional view taken on line B-B′ in FIG. 9([0097]b) to show the structure of the semiconductor device in FIGS.9(a) and9(b);
• FIG. 11 is a partially cutaway view in perspective of the structure of a semiconductor microactuator corresponding to a second embodiment of the invention;[0098]
• FIG. 12([0099]a) is a sectional view to show the structure of the semiconductor microactuator in FIG. 11 and FIG. 12(b) is a top view to show the structure of the semiconductor microactuator in FIG.
• FIG. 13 is a sectional view to show the structure of another semiconductor microactuator;[0100]
• FIGS.[0101]14(a) to14(e) are sectional views to show a manufacturing method of the semiconductor microactuator in FIG. 13;
• FIGS.[0102]15(a) to15(e) are sectional views to show a manufacturing method of the semiconductor microactuator in FIG. 13;
• FIG. 16 is a sectional view to show another wiring structure of the semiconductor microactuator in FIG. 13;[0103]
• FIG. 17 is a partially cutaway view in perspective of the structure of a semiconductor microactuator corresponding to a third embodiment of the invention;[0104]
• FIG. 18 is a top view to show the structure of the semiconductor microactuator corresponding to the third embodiment of the invention;[0105]
• FIG. 19 is a partially cutaway view in perspective of the structure of a semiconductor microactuator corresponding to a fourth embodiment of the invention;[0106]
• FIG. 20 is a top view to show the structure of the semiconductor microactuator corresponding to the fourth embodiment of the invention;[0107]
• FIG. 21 is a partially cutaway view in perspective of the structure of a semiconductor microactuator corresponding to a fifth embodiment of the invention;[0108]
• FIG. 22 is a top view to show the structure of the semiconductor microactuator corresponding to the fifth embodiment of the invention;[0109]
• FIG. 23 is a partially cutaway view in perspective of the structure of a semiconductor microactuator corresponding to a sixth embodiment of the invention;[0110]
• FIG. 24 is a partially cutaway view in perspective of the structure of a semiconductor microactuator corresponding to a seventh embodiment of the invention;[0111]
• FIG. 25 is a partially cutaway view in perspective of the structure of a semiconductor microactuator corresponding to an eighth embodiment of the invention;[0112]
• FIG. 26 is a partially cutaway view in perspective of the structure of another semiconductor microactuator;[0113]
• FIG. 27 is a partially cutaway view in perspective of the structure of a semiconductor microvalve corresponding to a ninth embodiment of the invention;[0114]
• FIG. 28 is a partially cutaway view in perspective of the structure of another semiconductor microvalve;[0115]
• FIG. 29 is a partially cutaway view in perspective of the structure of still another semiconductor microvalve;[0116]
• FIG. 30 is a partially cutaway view in perspective of the structure of a semiconductor microvalve corresponding to a tenth embodiment of the invention;[0117]
• FIG. 31 is a partially cutaway view in perspective of the structure of another semiconductor microvalve;[0118]
• FIG. 32 is a partially cutaway view in perspective of the structure of a semiconductor microrelay corresponding to an eleventh embodiment of the invention;[0119]
• FIG. 33 is a partially cutaway view in perspective of the structure of a semiconductor microrelay corresponding to a twelfth embodiment of the invention;[0120]
• FIGS.[0121]34(a) to34(d) are sectional views to show a manufacturing method of the semiconductor microrelay in FIG. 33;
• FIGS.[0122]35(a) to35(e) are sectional views to show a manufacturing method of the semiconductor microrelay in FIG. 33;
• FIGS.[0123]36(a) and36(b) are sectional views to show a manufacturing method of the semiconductor microrelay in FIG. 33;
• FIG. 37 is a partially cutaway view in perspective of the structure of another semiconductor microrelay;[0124]
• FIG. 38 is a perspective view used to describe the function of the semiconductor microrelay in FIG. 33;[0125]
• FIG. 39 is a relation drawing used to describe the function of the semiconductor microrelay in FIG. 33;[0126]
• FIG. 40 is a side view used to describe the function of the semiconductor microrelay in FIG. 33;[0127]
• FIG. 41 is a partially cutaway view in perspective of the structure of a semiconductor microrelay corresponding to a thirteenth embodiment of the invention;[0128]
• FIGS.[0129]42(a) to42(d) are sectional views to show a manufacturing method of the semiconductor microrelay in FIG. 41;
• FIGS.[0130]43(a) to43(e) are sectional views to show a manufacturing method of the semiconductor microrelay in FIG. 41;
• FIGS.[0131]44(a) and44(b) are sectional views to show a manufacturing method of the semiconductor microrelay in FIG. 33;
• FIGS.[0132]45(a) to45(d) are sectional views to show another manufacturing method of the semiconductor microrelay in FIG. 41;
• FIGS.[0133]46(a) to46(e) are sectional views to show another manufacturing method of the semiconductor microrelay in FIG. 41;
• FIGS.[0134]47(a) and47(b) are sectional views to show another manufacturing method of the semiconductor microrelay in FIG. 33;
• FIG. 48 is a partially cutaway view in perspective of the structure of another semiconductor microrelay;[0135]
• FIG. 49 is a perspective view used to describe the function of the semiconductor microrelay in FIG. 41;[0136]
• FIG. 50 is a relation drawing used to describe the function of the semiconductor microrelay in FIG. 41;[0137]
• FIG. 51 is a relation drawing used to describe the function of the semiconductor microrelay in FIG. 41;[0138]
• FIG. 52 is a partially cutaway view in perspective of the structure of another semiconductor microrelay;[0139]
• FIG. 53 is a top view to show the structure of a semiconductor microactuator in a related art;[0140]
• FIG. 54 is a sectional view to show the structure of the semiconductor microactuator in the related art;[0141]
• FIG. 55 is a sectional view to show the structure of a semiconductor microrelay in a related art; and[0142]
• FIG. 56 is a schematic drawing used to describe the function of the semiconductor microrelay in the related art.[0143]
• FIG. 57 is a partially cutaway view in perspective of the structure of a semiconductor microactuator using a semiconductor device corresponding to another embodiment of the invention;[0144]
• FIG. 58([0145]b) is a sectional view to show the structure of the semiconductor microactuator in FIG. 57;
• FIG. 58([0146]b) is a top view to show the structure of the semiconductor microactuator in FIG. 57;
• FIG. 59 is a partially cutaway view in perspective of the structure of a semiconductor microactuator using a semiconductor device corresponding to another embodiment of the invention;[0147]
• FIG. 60 is a top view to show the structure of the semiconductor microactuator in FIG. 59;[0148]
• FIG. 61 is a partially cutaway view in perspective of the structure of a semiconductor microvalve using a semiconductor device corresponding to another embodiment of the invention; and[0149]
• FIG. 62 is a partially cutaway view in perspective of the structure of a semiconductor microvalve using a semiconductor device corresponding to another embodiment of the invention.[0150]
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• Principal of Present Invention[0151]
• However, the semiconductor microactuator having the structure shown in U.S. Pat. No. 5,069,419 involves the following problem: First, the thermal insulation effect of the hinge structure of the silicon dioxide thin film will be considered. Generally, heat quantity Q escaping from a high-temperature portion to a low-temperature portion is[0152]
• Q(W)=−λ(t₂−t₁)/δ)A  (Expression X)
• where[0153]
• Q: Heat quantity (heat move speed)[0154]
• t[0155]₂−t₁: Temperature difference (° C)
• λ: Distance from heat source (cm)[0156]
• A: Cross section perpendicular to direction of heat flow (cm[0157]²)
• λ: Heat conductivity (J/cm s ° C)[0158]
• Then, the relational expression is used to calculate the heat quantity escaping from the[0159]diaphragm300 to thesilicon frame302. Letting the temperature difference between thediaphragm300 and thesilicon frame302 be 150° C., the width of thehinge303 be 30 μm, the diameter of thediaphragm200 be 2.5 mm, and the thickness of thehinge303 be 2 μm (estimated from “Electrically-Activated, Micromachined Diaphragm Valves” Technical Digest IEEE Solid-State Sensor and Actuator Workshop, pp65-69, June 1990), cross section perpendicular to the direction of heat flow, A1, is
• A1=2.5mm×π×2μm=0.25cm×π×2×10⁻⁴cm=1.57×10⁻⁴cm²
• Since the heat conductivity X of silicon dioxide equals 0.0084 (W/cm ° C.), escape heat quantity Q1 is[0160]$\mathrm{Q1}=0.084\left(W\text{/}{\mathrm{cm}}^{°}C.\right)\times {150}^{°}C./\left(30\times {10}^{-4}\mathrm{cm}\right)\times 1.57\times {10}^{-4}{\mathrm{<figure-callout\; label="cm"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">cm</figure-callout>}}^2=0.66W=600\mathrm{mW}$

  
• Next, the heat quantity escaping from the[0161]diaphragm300 to thesilicon frame302 if the hinge structure of silicon dioxide is not provided is calculated. Letting the thickness of thesilicon diaphragm300 be 10 μm, cross section perpendicular to the direction of heat flow, A2, is calculated as follows:
• A2=2.5mm×π×10μm=0.25cm×π×10×10⁻⁴cm=7.85×10⁻⁴cm²
• Since the heat conductivity λ of silicon equals 1.48 (W/cm ° C.), escape heat quantity Q2 is[0162]
• Q2=1.48(W/cm ° C.)×150° C./(30×10⁻⁴cm)×7.85×10⁻⁴_cm²=58W
• Then, the[0163]hinge303 of silicon dioxide thin film is provided, whereby about 90-times thermal insulation effect can be produced. Thus, the semiconductor microactuator described in U.S. Pat. No. 5,069,419 has a structure with better thermal efficiency than that of the conventional structure. However, considering the current state of application, it is desired to furthermore decrease the heat loss. Specifically, the heat escape (heat loss) is thought of as power (consumption power) supplied all the time to maintain thediaphragm300 at a predetermined temperature (for example, 150° C.).
• In the semiconductor microactuator described in U.S. Pat. No. 5,069,419, the silicon dioxide thin film is thick as 2 μm in the part of the[0164]hinge303. The factor for determining the thickness of the silicon dioxide thin film of thehinge303 is not clearly described in the specification. However, if the semiconductor microactuator described in U.S. Pat. No. 5,069,419 is used with a microvalve, etc., it is conceivable that pressure applied to a moving element will concentrate on thehinge303, and a film thickness is required to such an extent that thehinge303 is not broken under the pressure. However, if the film thickness of thehinge303 is increased, the thermal insulation effect is reduced as shown in the heat escape calculation expression (expression X). Then, it can be estimated that the thickness of the silicon dioxide thin film having a reasonable strength and producing a thermal insulation effect is determined 2 μm.
• By the way, the semiconductor microactuator described in U.S. Pat. No. 5,069,419 is of a moving structure with bimetal made up of the[0165]silicon diaphragm300 and the aluminumthin film304 as described in the specification; to provide electric insulation, a silicon dioxidethin film306 is inserted between thediaphragm300 and the aluminumthin film304.
• In a semiconductor manufacturing process, it is desired that the silicon dioxide[0166]thin film306 and the silicon dioxide thin film of thehinge303 are formed at the same time and have the same film thickness. However, if the film thickness of the silicon dioxidethin film306 inserted between thediaphragm300 and the aluminumthin film304 becomes thick as 2 μm, it is conceivable that the bimetal characteristic of the drive source will degraded. In the example described in the document “Electrically-Activated, Micromachined Diaphragm Valves” Technical Digest IEEE Solid-State Sensor and Actuator Workshop, pp65-69, June 1990, the aluminumthin film304 has a film thickness of 5 to 6 μm and if the silicon dioxidethin film306 having a film thickness of 2 μm is inserted between thediaphragm300 and the aluminumthin film304, it can be easily estimated that the silicon dioxidethin film306 will become a factor for hindering bending of thediaphragm300 at the heating time.
• In the semiconductor manufacturing process, normally a thin film of silicon dioxide is formed at a high temperature of about 2000° C. Thus, considering the thermal expansion coefficients of silicon and silicon dioxide, it is possible that a considerable internal stress occurs between the[0167]silicon diaphragm300 and the silicon dioxidethin film306. As the silicon dioxidethin film306 becomes thicker, the internal stress grows, causing the bimetal characteristic to be degraded. Thus, the silicon dioxidethin film306 between thediaphragm300 and the aluminumthin film304 must be thinned as much as possible (2×10⁻⁸m (200 A)) and the silicon dioxide film of thehinge303 must be made thick to some extent (2 μm). However, formation of such a thin film structure of silicon dioxide requires a very complicated semiconductor manufacturing process. The manufacturing process is not mentioned in the specification of U.S. Pat. No. 5,069,419.
• As a remedy, another hinge structure is disclosed in U.S. Pat. No. 5,271,597, wherein the thin film structure of silicon dioxide as described above is not adopted and a silicon dioxide thin film of a hinge part and a silicon dioxide thin film between a diaphragm and an aluminum thin film have the same film thickness. In this method, the silicon dioxide thin film of the hinge part is thinned and to make up for reduction in the strength of the hinge part as the film is thinned, silicon of a part of the diaphragm is used for bonding the diaphragm and a silicon frame in addition to the hinge, thus the thermal insulation effect is reduced and a structure for lessening power consumption of the semiconductor microactuator is not provided. Thus, a large number of problems remain to be solved in the thermal insulation structure in the semiconductor microactuator.[0168]
• As an example of a semiconductor microvalve in a related art, a microminiature valve is described in U.S. Pat. No. 5,058,856. This microminiature valve also uses a semiconductor microactuator comprising at least two materials having different thermal expansion coefficients in combination as a bimetal structure wherein the bimetal structure is heated and the difference between the thermal expansion coefficients is used to provide displacement. The microactuator has a thermal insulation structure provided by placing a torsion bar suspension. This structure minimizes the heat loss to a silicon frame because of a decrease in the cross section perpendicular to a heat flow and an increase in the length of a passage through which the heat flow passes. However, since the torsion bar suspension structure is formed of silicon, it is considered that a sufficient thermal insulation effect cannot be produced as discussed in the calculation of heat escape.[0169]
• This can be estimated from a microvalve performance comparison table described in the document “SILICON MICROVALVES FOR GAS FLOW CONTROL” The 8th International Conference on Solid-State Sensor and Actuators, Stockholm, Sweden, 1995, p276-279. This document compares a microvalve involving the “semiconductor microactuator” disclosed in U.S. Pat. No. 5,069,419 with a microvalve related to the “microminiature valve” disclosed in U.S. Pat. No. 5,058,856; the latter has pressure resistance six times that of the former and flow[0170]quantity range 10 times that of the former, but power consumption about twice that of the former and heat resistance about a third that of the former.
• Thus, the microminiature valve disclosed in U.S. Pat. No. 5,058,856 has a structure capable of generating a large force because of the torsion bar suspension structure formed of silicon, but consumes larger power.[0171]
• First Embodiment[0172]
• A first embodiment of the invention will be discussed. FIG. 1 is a partially cutaway view in perspective of the structure of a semiconductor microactuator using a semiconductor device according to the invention. FIG. 2A is a sectional view and FIG. 2B is a top view.[0173]
• As shown in the figures, a[0174]semiconductor microactuator1 includes asemiconductor substrate3 which becomes a hollow frame shaped roughly like a quadrangle, fourthin portions2S each shaped roughly like a quadrangle piece, thethin portions2S separated from thesemiconductor substrate3 with one ends connected viathermal insulation areas7 inwardly roughly from the centers of the sides of thesemiconductor substrate3, a movingelement5 formed like a hollow quadrangular prismoid with the top face opened like a quadrangle and narrower toward the bottom, the movingelement5 having top opening margins connected to opposite ends of thethin portions2S, andthin films2M of aluminum thin films, nickel thin films, or the like placed on the top faces of thethin portions2S, thethin films2M and thethin portions2S making upflexible areas2.
• The[0175]semiconductor substrate3, the thin portions2s, and the movingelement5 are formed, for example, by working a semiconductor substrate of a silicon substrate, etc. Eachthin portion2S is formed on a surface with an impurity-diffused resistor6 (diffused resistor6) of heating means. Power is supplied to the diffusedresistors6 by wiring4aconnected toelectrode pads4 placed at the four corners of thesemiconductor substrate3 and the temperatures of the diffusedresistors6 rise, heating theflexible areas2 each made up of thethin portion2S and thethin film2M. Thethin film2M is made of aluminum, nickel, or the like as described above and thethin portion2S is made of silicon, etc.; thethin film2M and thethin portion2S have different thermal expansion coefficients.
• Each[0176]thermal insulation area7 for joining thesemiconductor substrate3 and theflexible area2 has roughly the same thickness as thethin portion2S and is made of a thermal insulation material such as a fluoridated resin or polyimide for thermally insulating thesemiconductor substrate3 and theflexible area2. Of theelectrode pads4 placed at the four corners of thesemiconductor substrate3, theelectrode pads4 in the upper-right corner and the lower-left corner in FIG. 2B are connected to an external power supply and the series circuit of two diffusedresistors6 is connected in parallel to power supply.
• The four[0177]flexible areas2 are in the shape of a cross with the movingelement5 at the center and the surroundings of the movingelement5 are supported by theflexible areas2. Thesemiconductor substrate3, theflexible areas2, and thethermal insulation areas7 each between thesemiconductor substrate3 and theflexible area2 make up asemiconductor device8.
• In the described[0178]semiconductor microactuator1, upon application of power to the diffusedresistors6, the temperature rises, heating theflexible areas2, and a thermal stress occurs because of the difference between the thermal expansion coefficients of thethin film2M and thethin portion2S making up eachflexible area2. For example, if metal thin films of aluminum, nickel, etc., are formed as thethin films2M, the metal of aluminum, nickel, etc., has a lager thermal expansion coefficient than silicon forming thethin portions2S, so that theflexible areas2 are bent downward in the figure. The movingelement5 placed contiguous with theflexible areas2 receives the thermal stress of theflexible areas2 and is displaced downward with respect to thesemiconductor substrate3.
• As described above, the[0179]semiconductor microactuator1 includes the fourflexible areas2 in the shape of a cross with the movingelement5 at the center and displacement of the movingelement5 becomes irrotational displacement relative to thesemiconductor substrate3; good control accuracy of displacement is provided and a large force can be generated. As described above, eachflexible area2 is formed on the surface with the diffusedresistor6 for heating theflexible area2, namely, contains the diffusedresistor6, so that thesemiconductor microactuator1 can be miniaturized.
• The[0180]semiconductor microactuator1 of the embodiment includes eachflexible area2 made up of two areas having different thermal expansion coefficients, namely, thethin portion2S and thethin film2M, but the invention is not limited to it. For example, eachflexible area2 may be made of a shape memory alloy of nickel titanium, etc., and theflexible area2 made of a shape memory alloy may be displaced because of temperature change.
• Of course, this invention is limited for use of semiconductor microactuator. It is applicable for a temperature sensor in such a manner that the displacement of the flexible area caused by changing the temperature is measured by, for example, the laser displacement device to detect the temperature in accordance with the displacement of the flexible area. Namely the present invnetion is applied to the semiconductor device using the effect such that the[0181]thermal insulation area7 is provided between eachflexible area2 and thesemiconductor substrate3, so that thesemiconductor microactuator1 has the advantage that heat produced when theflexible areas2 are heated can be prevented from escaping to thesemiconductor substrate3.
• To describe the function of the[0182]semiconductor device8 used with thesemiconductor microactuator1 of the invention, the case where the length and the thickness in the joint direction of thesemiconductor substrate3 and theflexible area2 in thethermal insulation area7 are 30 μm and 20 μm respectively and polyimide is used as the material as shown in FIG. 3, which is a sectional view of thesemiconductor device8, will be discussed as a specific example. Assume that the length in the joint direction of theflexible area2 shown in FIG. 1 is 800 μm and the width of the flexible area2 (length in the direction orthogonal to the joint direction) is 600 μm.
• Heat quantity Q3 escaped from the[0183]flexible area2 through thethermal insulation area7 to thesemiconductor substrate3 is calculated according to the expression X shown in the description of the related art. Here, cross section perpendicular to the direction of the heat flow of escape heat, A10, is
• A10=(thickness of polyimide)×(width of flexible area)=20μm×600μm=1.2×10⁻⁴cm²
• The heat conductivity of polyimide is 1.17×10[0184]⁻³(W/cm ° C) and the distance from the heat source, δ, namely, the distance between theflexible area2 and thesemiconductor substrate3 is 30 μm. Thus, the heat quantity Q3 escaped from theflexible area2 heated to 150° C. to thesemiconductor substrate3 is$\mathrm{Q3}=1.17\times {10}^{-3}\left(W\text{/}{\mathrm{cm}}^{°}C.\right)\times \left({150}^{°}C./\left(30\times {10}^{-4}\mathrm{cm}\right)\right)\times 1.2\times {10}^{-4}\left({\mathrm{cm}}^2\right)=4.2\times {10}^{-3}\left(W\right)=4.2\left(\mathrm{mW}\right)$

  
• Since the[0185]semiconductor device8 has the fourflexible areas2 as described above, the heat quantity becomes 16.8 mW as a whole. This indicates that the temperature of theflexible area2 can be maintained at 150° C. by feeding input power 16.8 mW into the diffusedresistor6; the power consumption can be reduced to {fraction (1/40)} as compared with 660 mW in the related art.
• Next, the strength of the[0186]thermal insulation area7 made of polyimide will be discussed. A model of a twin-cantilever structure with both ends fixed shown in FIG. 4A will be considered. If load W is imposed on the center of a beam21 (corresponding to the flexible area2) from below as shown in FIG. 4A, the shearing force and moment force of thebeam21 become as shown in FIGS. 4B and 4C respectively. In FIG. 4A, thethermal insulation area7 is positioned either between afixed end22aand thebeam21 or between afixed end22band thebeam21. Then, a force applied to thebeam21 is found, for example, if l-g load W is imposed on the center of the beam21 (corresponding to the case where a pressure of 46.7 kPa is put on an orifice 500 μm for a microvalve).
• Shearing force applied to the beam, F1, is[0187]
• F1=W/2=1.0×10[0188]⁻³(kgf)/2=0.5×10⁻³(kgf)=4.9×10⁻³(N), and maximum shearing strength applied to the beam, Fmax, is Fmax=F1/S1 (where S1 is the cross-sectional area of the beam). Here, letting width b1 of thebeam21 be 600 μm and thickness hi of thebeam21 be 20 μm, the cross-sectional area S1 is
• S1=(b1)(h1)=600×10[0189]⁻4×20×10⁻⁴=1.2×10⁻⁴cm². Therefore, the maximum shearing strength applied to thebeam21, Fmax, is Fmax=0.50×10⁻³(kgf)/1.2×10⁻⁴(cm²)=4.16 (kgf/cm²)=4.16×0.098 (MPa)=0.41 (MPa). Next, maximum stress applied to thebeam21, σmax, is found. The maximum stress σmax is represented as σmax=Mmax/Z1 where Mmax is the maximum moment and Z1 is a section modulus. The maximum moment Mmax equals WL/8 (where L is the length of the beam, 800 μm) as shown in FIG. 4C. Therefore, the maximum moment Mmax
• Mmax=WL/8=1.0×10[0190]⁻³(kgf)×800×10⁻⁴(cm)/8=1.0×10⁻⁵(kgf cm)=9.8×10⁻⁵(N cm). The section modulus Z1 is
• Z1=(b1)(h1)[0191]²/6=⅙×600×10⁻⁴×(20×10⁻⁴)2=4.0×10⁻⁸(cm³). Then, the maximum stress σmax based on the moment is$\sigma \max =M\max /Z=1.0\times {10}^{-5}\left(\mathrm{kgf}\mathrm{cm}\right)/4.0\times {10}^{-8}\left({\mathrm{cm}}^3\right)=250\left(\mathrm{kgf}\text{/}{\mathrm{cm}}^2\right)=24.5\left(\mathrm{MPa}\right).$

  
• The[0192]beam21 is 600 μm wide and 800 μm long as described above.
• Since polyimide has a disruptive strength of about 30 MPa, a semiconductor microactuator capable of resisting a load of about 1 g in the[0193]thermal insulation area7 described above can be provided. The strength of thethermal insulation area7 can be enhanced as shown in another example. Although not described, a similar advantage can also be expected with a fluoridated resin.
• A formation method example of the[0194]thermal insulation area7 will be discussed with reference to FIGS. 5A to5D. First, as shown in FIG. 5A, the portion corresponding to a thermal insulation area on the surface of asemiconductor substrate17 is etched with KOH, etc., to form agroove15. Then, as shown in FIG. 5B, a coat of a polyimidethin film16 is rotationally applied with a coater, etc., so as to fill thegroove15. Next, as shown in FIG. 5C, patterning is performed by executing a semiconductor photolithography process, etc., so that the polyimidethin film16 of the portion filling thegroove15 is left and that other portions are removed, and heating is executed to about 400° C. to evaporate an organic solvent, etc., contained in polyimide and cure. Next, as shown in FIG. 5D, etching with KOH, etc., is performed from the rear face of thesemiconductor substrate17. In FIG. 5D, numeral19 denotes a semiconductor substrate which becomes a frame and numeral20 denotes a flexible area. Thethermal insulation area7 is formed through such a process.
• Thus, the[0195]thermal insulation area7 is formed between theflexible area2 and thesemiconductor substrate8 utilizing the nature that the resin material of polyimide, fluoridated resin, etc., has high thermal insulation properties (thermal conductivity coefficient: 0.4 W/(m ° C.) or less, about 80 times that of silicon dioxide) and is liquid and easy to work and can be easily formed to be a thin film of a desired thickness (several μm to several ten μm) by executing a semiconductor manufacturing process of spin coat, etc. Therefore, a semiconductor device having an excellent thermal insulation effect and strength as compared with the example in the related art can be easily provided using the semiconductor manufacturing process. As described above, thethermal insulation area7 is made almost as thick as thethin portion2S of theflexible area2, whereby thesemiconductor substrate3 and theflexible area2 are joined reliably and the strength of the joint portion can be enhanced.
• The[0196]semiconductor microactuator1 using thesemiconductor device8 comprising such advantages, which is easily manufactured and has high thermal insulation properties, prevents heat generated by the diffusedresistors6 from escaping and can be driven with low power consumption, namely, can be driven with a battery and thus can be miniaturized.
• Next, another configuration example of the[0197]semiconductor device8 will be discussed. As shown in FIGS. 6A and 6B, theexample semiconductor device8 is the same as the semiconductor device in FIG. 3 in that athermal insulation area7 made of a thermal insulation material such as a fluoridated resin or polyimide is formed between asemiconductor substrate3 and aflexible area2; the former differs from the latter in that thethermal insulation area7 is formed on a bottom face (face orthogonal to the thickness direction) with areinforcement layer12 made of a harder material than the material forming thethermal insulation area7, such as a silicon dioxide thin film (Young's modulus: 9.8×10⁻⁹N/m²or more). FIG. 6A is a sectional view and FIG. 6B is a top view. FIG. 7 is a sectional view taken on line Y-Y′ in FIG. 6B.
• Specifically, as shown in FIG. 7, the[0198]thermal insulation area7 is 19 μm thick and thereinforcement layer12 is 1 μm thick. As shown in FIG. 6A, the length in the joint direction of thesemiconductor substrate3 and theflexible area2 in thethermal insulation area7 is 30 μm and the length in the Y-Y′ direction, namely, in the depth direction is 600 μm. Here, the strength of thethermal insulation area7 to use polyimide as the material forming thethermal insulation area7 and silicon dioxide as the material forming thereinforcement layer12 is calculated under similar conditions to those of the strength calculation of thethermal insulation area7 in FIG. 3 described above.
• Letting the Young's modulus of the material of each of the[0199]thermal insulation area7 and thereinforcement layer12 be E_iand the cross-sectional area of the cross section of each area shown in FIG. 7 be A_i, the distance from the bottom face to the neutral axis, ηa, is given by the following expression:$\begin{array}{cc}\eta a_i=\frac{\sum _i^{}E_i\int \eta {\mathrm{dA}}_i}{\sum _i^{}E_i·A_i}& \left[\mathrm{Expression}1\right]\end{array}$

  
• The values are found with respect to silicon dioxide forming the[0200]reinforcement layer12 as follows:$\begin{array}{cc}\mathrm{Young}\text{'}s\mathrm{modulus}E_s;7.3\times {10}^{10}\left(N/m^2\right)\mathrm{Cross}\text{-}\mathrm{sectional}\mathrm{area}A_s;1\times {10}^{-6}\times 600\times {10}^{-6}\left(m^2\right)E_s·A_s=7.3\times {10}^{10}\left(N/m^2\right)\times 1\times {10}^{-6}\times 600\times {10}^{-6}\left(m^2\right)=43.8N\begin{array}{c}{E}_s\int \eta {\mathrm{dA}}_s=E_s{\int }_0^{1\mu m}\eta \left(600\times {10}^{-6}d\eta \right)\\ =7.3\times 6\times {10}^6\times {\left[{\mathrm{<figure-callout\; label="\eta "\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">\eta </figure-callout>}}^2/2\right]}_0^{1\mu m}\\ =21.9\times {10}^{-6}N-m\end{array}& \left[\mathrm{Expression}2\right]\end{array}$

  
• The values are found with respect to polyimide forming the[0201]thermal insulation area7 as follows:$\begin{array}{cc}\mathrm{Young}\text{'}s\mathrm{modulus}E_f;5.0\times {10}^8\left(N/m^2\right)\mathrm{Cross}\text{-}\mathrm{sectional}\mathrm{area}A_f;19\times {10}^{-6}\times 600\times {10}^{-6}\left(m^2\right)E_f·A_f=5.0\times {10}^8\left(N/m^2\right)\times 19\times {10}^{-6}\times 600\times {10}^{-6}\left(m^2\right)=5.70N\begin{array}{c}{E}_f\int \eta {\mathrm{dA}}_f=E_f{\int }_{1\mu m}^{20\mu m}\eta \left(600\times {10}^{-6}d\eta \right)\\ =5.0\times 6\times {10}^4\times {\left[{\mathrm{<figure-callout\; label="\eta "\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">\eta </figure-callout>}}^2/2\right]}_{1\mu m}^{20\mu m}\\ =59.8\times {10}^{-6}N\text{-}m\end{array}& \left[\mathrm{Expression}3\right]\end{array}$

  
• Using the found values, the distance to the neutral axis, ηa, is found as follows:[0202]$\begin{array}{cc}\eta a=\frac{\sum _i^{}E_i\int \eta {\mathrm{dA}}_i}{\sum _i^{}E_i·A_i}=\frac{\left(21.9+59.8\right)\times {10}^{-6}}{\left(42.8+5.7\right)}=1.68\times {10}^{-6}\left(m\right)=1.68\mathrm{\mu m}& \left[\mathrm{Expression}4\right]\end{array}$

  
• Next, secondary moments I[0203]_sand I_fconcerning the neutral axes of silicon dioxide and polyimide are found as follows:$\begin{array}{cc}\begin{array}{c}{I}_s=\int {\eta }_i^2{\mathrm{dA}}_i={\int }_{0.66\mathrm{\mu m}}^{1.68\mathrm{\mu m}}{\eta }_i^2\left(600\times {10}^{-6}d{\eta }_i\right)\\ =600\times {10}^{-6}\times {\left[{\mathrm{<figure-callout\; label="\eta "\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">\eta </figure-callout>}}^3/3\right]}_{-0.68\mathrm{\mu m}}^{1.68\mathrm{\mu m}}\\ =8.86\times {10}^{-22}{\mathrm{<figure-callout\; label="m"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">m</figure-callout>}}^4\end{array}\begin{array}{c}{I}_f=\int {\eta }_i^2{\mathrm{dA}}_i={\int }_{0.68\mathrm{\mu m}}^{18.32\mathrm{\mu m}}{\eta }_i^2\left(600\times {10}^{-6}d{\eta }_i\right)\\ =600\times {10}^{-6}\times {\left[{\mathrm{<figure-callout\; label="\eta "\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">\eta </figure-callout>}}^3/3\right]}_{-0.68\mathrm{\mu m}}^{18.32\mathrm{\mu m}}\\ =1.22\times {10}^{-18}m^4\end{array}& \left[\mathrm{Expression}5\right]\end{array}$

  
• Here, ηi=η−ηa, namely, ηi denotes the distance from the neutral axis. As previously described with reference to FIGS. 4A to[0204]4C, if a load of 1 g is imposed on the center of the beam with both ends fixed, the maximum moment Mmax applied to the beam is Mmax=1.00×10⁻⁵(kgf cm)=9.8×1.00×10⁻5×10⁻²(N m)=9.8×10⁻⁷(N m).
• The maximum bending stress of silicon dioxide, σsmax, is calculated as follows:[0205]$\begin{array}{cc}\begin{array}{c}{\sigma }_{s\max }=M_{\max }\frac{E_s·{\eta }_i}{\sum _i^{}E_i·I_i}\\ =\frac{0.98\times {10}^{-6}\times 7.3\times {10}^{10}\times 1.68\times {10}^{-6}}{7.3\times {10}^{10}\times 8.86\times {10}^{-22}+5\times {10}^8\times 1.22\times {10}^{-18}}\\ =1.78\times {10}^8\left(\mathrm{kg}\text{/}m^2\right)=178\left(\mathrm{MPa}\right)\end{array}& \left[\mathrm{Expression}6\right]\end{array}$

  
• Here, I[0206]_idenotes each of the secondary moments I_sand I_f. The maximum bending stress of polyimide, σfmax, is calculated as follows:$\begin{array}{cc}\begin{array}{c}{\sigma }_{f\max }=M_{\max }\frac{E_f·{\eta }_i}{\sum _i^{}E_i·I_i}\\ =\frac{0.98\times {10}^{-6}\times 5.0\times {10}^8\times 18.32\times {10}^{-6}}{7.3\times {10}^{10}\times 8.86\times {10}^{-22}+5\times {10}^8\times 1.22\times {10}^{-18}}\\ =1.33\times {10}^7\left(\mathrm{kg}\text{/}m^2\right)=13.3\left(\mathrm{MPa}\right)\end{array}& \left[\mathrm{Expression}7\right]\end{array}$

  
• Therefore, the stress applied to the[0207]thermal insulation area7 made of polyimide becomes about a half that in the example shown in FIG. 3. Apparently, it is equivalent to twice the strength. In FIG. 6, thereinforcement layer12 is provided on the bottom face of thethermal insulation area7, but if thereinforcement layer12 is provided on the top face of thethermal insulation area7, a similar effect can be produced if the direction is a direction orthogonal to the thickness direction. If thereinforcement layer12 is provided on both the top and bottom faces of thethermal insulation area7, twice the effect produced by providing thereinforcement layer12 on either the top or bottom face of thethermal insulation area7 can be produced.
• A formation method example of the[0208]thermal insulation area7 shown in FIGS. 6A and 6B will be discussed with reference to FIGS. 8A to8E. First, as shown in FIG. 8A, the portion corresponding to a thermal insulation area on the surface of asemiconductor substrate17ais etched with KOH, etc., to form agroove15a. Then, as shown in FIG. 8B, a silicon dioxidethin film18 is formed on the surface of thesemiconductor substrate17aby thermal oxidation, etc. The silicon dioxidethin film18 is removed except the surface portion of thegroove15aby etching, etc.
• Next, as shown in FIG. 8C, a coat of a polyimide[0209]thin film16ais rotationally applied with a coater, etc., so as to fill thegroove15a. Next, as shown in FIG. 8D, patterning is performed by executing a semiconductor photolithography process, etc., so that the polyimidethin film16aof the portion filling thegroove15ais left and that other portions are removed, and heating is executed to about 400° C. to evaporate an organic solvent, etc., contained in polyimide and cure. Next, as shown in FIG. 8E, etching with KOH, etc., is performed from the rear face of thesemiconductor substrate17a, thereby forming the thermal insulation area. In FIG. 8E, numeral19adenotes a semiconductor substrate which becomes a frame and numeral20adenotes a flexible area.
• Next, still another configuration example of semiconductor device of the invention will be discussed. As shown in FIG. 9B, which is a top view, a[0210]thermal insulation area10 is provided between asemiconductor substrate3 and aflexible area2 and the portions of thesemiconductor substrate3 and theflexible area2 in contact with thethermal insulation area10 form comb teeth in the joint direction of thesemiconductor substrate3 and the flexible area2 (orthogonal direction to line B-B′). As shown in FIG. 10, which is a sectional view taken on line B-B′ in FIG. 9B, theflexible area2, thesemiconductor substrate3, and thethermal insulation area10 are mixed in the B-B′ direction. Thethermal insulation area10 is formed of a fluoridated resin, polyimide, etc.
• To calculate the strength of the[0211]thermal insulation area10, let the thickness of thethermal insulation area10 be 20 μm and the width in a direction perpendicular to the B-B′ direction be 30 μm, as shown in FIGS. 9A and 9B, as a specific example. As shown in FIG. 10, let the width in the B-B′ direction of each comb tooth consisting of theflexible area2 and thesemiconductor substrate3 be 180 μm and the width in the B-B′ direction of thethermal insulation area10 be 30 μm. The material of thethermal insulation area10 is polyimide and thesemiconductor substrate3 and theflexible area2 are formed of silicon. The strength of thethermal insulation area10 is calculated under similar conditions to those of the strength calculation in FIG. 3 for comparison.
• For a structure comprising silicon and polyimide in combination as shown in FIG. 10, letting the Young's modulus of silicon be E[0212]_si, the Young's modulus of polyimide be E_ph, the secondary moment of the cross section of the silicon part be I_si, the secondary moment of the cross section of the polyimide part be I_ph, the moment applied to the silicon part be M_si, and the moment applied to the polyimide part be M_ph, the following relational expression is involved:$\begin{array}{cc}\frac{1}{\rho }=\frac{M_{\mathrm{Si}}}{E_{\mathrm{Si}}·I_{\mathrm{Si}}}=\frac{M_{\mathrm{Ph}}}{E_{\mathrm{Ph}}·I_{\mathrm{Ph}}}=k\left(\mathrm{constant}\right)& \left[\mathrm{Expression}8\right]\end{array}$

  
• M_max=M_Si+M_Phρ:Curvature
• Then, the moment of the silicon part, M[0213]_si, and the moment of the polyimide part, M_ph, are represented by
• M_Si=k·E_Si·I_SiM_Ph=k·E_Ph·I_Ph$k=\frac{M_{\mathrm{Ph}}}{E_{\mathrm{Ph}}·I_{\mathrm{Ph}}}$

  
• Then, the moment applied to the whole of the thermal insulation structure, M[0214]_max, is$\begin{array}{c}{M}_{\max }=M_{\mathrm{Si}}+M_{\mathrm{Ph}}=k·E_{\mathrm{Si}}·I_{\mathrm{Si}}+M_{\mathrm{Ph}}\\ =\frac{E_{\mathrm{Si}}·I_{\mathrm{Si}}}{E_{\mathrm{Ph}}·I_{\mathrm{Ph}}}M_{\mathrm{Ph}}+M_{\mathrm{Ph}}\end{array}$

  
• [Expression 9][0215]
• The moment of the polyimide part, M[0216]_ph, is$M_{\mathrm{Ph}}=\frac{M_{\max }}{\frac{E_{\mathrm{Si}}·I_{\mathrm{Si}}}{E_{\mathrm{Ph}}·I_{\mathrm{Ph}}}+1}$

  
• Likewise, the moment of the silicon part, M[0217]_si, is$M_{\mathrm{Si}}=\frac{M_{\max }}{\frac{E_{\mathrm{Ph}}·I_{\mathrm{Ph}}}{E_{\mathrm{Si}}·I_{\mathrm{Si}}}+1}$

  
• The values concerning the silicon part and the polyimide part are calculated.[0218]
• Young's modulus of silicon,E_si,=0.19×10⁻¹²(N/m²)=1.9×10⁻¹²(dyne/cm²)$\begin{array}{cc}\begin{array}{c}{E}_{\mathrm{Si}}=1.9\times {10}^{12}\left(\mathrm{dyne}\text{/}{\mathrm{cm}}^2\right)\times 1.019\times {10}^{-6}=1.93\times {10}^6\mathrm{kgf}\text{/}{\mathrm{<figure-callout\; label="cm"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">cm</figure-callout>}}^2\\ I_{\mathrm{Si}}=\frac{1}{12}{\mathrm{<figure-callout\; label="bh"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">bh</figure-callout>}}^3=\frac{1}{12}\times 180\times 3\times {10}^{-4}\left(\mathrm{cm}\right)\times {\left(20\times {10}^{-4}\mathrm{cm}\right)}^3\\ =3.6\times {10}^{-11}{\mathrm{cm}}^4\end{array}& \left[\mathrm{Expression}10\right]\end{array}$

  
• Therefore, E[0219]_si$\begin{array}{c}{E}_{\mathrm{si}}I_{\mathrm{si}}=1.93\times 106\left(\mathrm{kgf}\text{/}{\mathrm{cm}}^2\right)\times 3.6\times {10}^{-11}\left({\mathrm{cm}}^4\right)=\\ 6.94\times {10}^{-5}\left(\mathrm{kgf}\text{/}{\mathrm{cm}}^2\right)=6.8\times {10}^{-4}N{\mathrm{<figure-callout\; label="cm"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">cm</figure-callout>}}^2.\end{array}$

  
• The Young's modulus of polyimide, E[0220]_ph, is 500 MPa$\begin{array}{cc}\begin{array}{c}{E}_{\mathrm{Ph}}=5.0\times {10}^6\left(\mathrm{Pa}\right)\times 1.019\times {10}^{-5}=5.10\times {10}^3\mathrm{kgf}\text{/}{\mathrm{cm}}^2\\ I_{\mathrm{Ph}}=\frac{1}{12}{\mathrm{<figure-callout\; label="bh"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">bh</figure-callout>}}^3=\frac{1}{12}\times 30\times 2\times {10}^{-4}\left(\mathrm{cm}\right)\times {\left(20\times {10}^{-4}\mathrm{cm}\right)}^3\\ =4.0\times {10}^{-12}{\mathrm{cm}}^4\end{array}& \left[\mathrm{Expression}11\right]\end{array}$

  
• Therefore, E[0221]_phI_ph=5.10×10³(kgf/cm²)×4×10⁻¹²(cm⁴)=2.04×10⁻⁸(kgf/cm²)=2.00×10⁻⁷(N cm²).
• The moment applied to the polyimide part, M[0222]_ph, is as follows:$\begin{array}{cc}{M}_{\mathrm{Ph}}=\frac{1.0\times {10}^{-5}\left(\mathrm{kgf}·\mathrm{cm}\right)}{\frac{6.94\times {10}^{-5}}{2.04\times {10}^{-8}}+1}=2.93\times {10}^{-9}\left(\mathrm{kgf}·\mathrm{cm}\right)& \left[\mathrm{Expression}12\right]\end{array}$

  
• M_ph=2.93×10⁻⁹(kgf cm)=2.87×10⁻⁸(N cm).
• Likewise, the moment applied to the silicon part, M[0223]_si, is as follows:$\begin{array}{cc}{M}_{\mathrm{Si}}=\frac{1.0\times {10}^{-5}\left(\mathrm{kgf}·\mathrm{cm}\right)}{\frac{2.04\times {10}^{-6}}{6.94\times {10}^{-5}}+1}=9.99\times {10}^{-6}\left(\mathrm{kgf}·\mathrm{cm}\right)& \left[\mathrm{Expression}13\right]\end{array}$

  
• M_si=9.99×10⁻⁶(kgf cm)=9.79×10⁻⁶(N cm).
• Then, the maximum stress applied to the polyimide part, σ[0224]_ph, is as follows:$\begin{array}{cc}\begin{array}{c}\mathrm{Za}=\frac{1}{6}{\mathrm{bh}}^2=2.0\times {10}^{-9}\left({\mathrm{cm}}^3\right)\\ {\sigma }_{\mathrm{Ph}}=\frac{M_{\mathrm{Ph}}}{\mathrm{Za}}=\frac{2.93\times {10}^{-9}\left(\mathrm{kgf}·\mathrm{cm}\right)}{3.8\times {10}^{-9}\left({\mathrm{cm}}^3\right)}=0.77\left(\mathrm{kgf}\text{/}{\mathrm{cm}}^2\right)=7.54\times {10}^{-2}\left(\mathrm{MPa}\right)\end{array}& \left[\mathrm{Expression}14\right]\end{array}$

  
• Here, Za is a section modulus. The maximum stress applied to the polyimide part, σ[0225]_si, is found as follows:$\begin{array}{cc}\mathrm{Zb}=\frac{1}{6}{\mathrm{bh}}^2=3.5\times {10}^{-8}\left({\mathrm{cm}}^3\right){\sigma }_{\mathrm{Si}}=\frac{M_{\mathrm{Si}}}{\mathrm{Zb}}=\frac{9.99\times {10}^{-6}\left(\mathrm{kgf}·\mathrm{cm}\right)}{3.6\times {10}^{-8}\left({\mathrm{cm}}^3\right)}=2.77\left(\mathrm{kgf}\text{/}{\mathrm{cm}}^2\right)=27\left(\mathrm{MPa}\right)& \left[\mathrm{Expression}15\right]\end{array}$

  
• Here, Zb is a section modulus.[0226]
• Therefore, the stress applied to the thermal insulation area made of polyimide becomes about {fraction (1/300)} that in the example shown in FIG. 3. Apparently, it is equivalent to 300 times the strength. In FIG. 9, the number of comb teeth formed by the[0227]semiconductor substrate3 and theflexible area2 is not limited to that shown in FIG. 9; a similar effect can be produced by providing a structure containing at least two comb teeth or more.
• Second Embodiment[0228]
• Next, a second embodiment of the invention will be discussed. FIG. 11 is a perspective view of a semiconductor microactuator in the first embodiment of the invention. FIG. 12A is a sectional view and FIG. 12B is a top view.[0229]
• A[0230]semiconductor microactuator1aof the second embodiment differs from the semiconductor microactuator previously described with reference to FIGS. 1 and 2 in that it includes a newthermal insulation area7A between aflexible area2 and a movingelement5 and that theflexible area2 and the movingelement5 are joined by thethermal insulation area7A.
• The[0231]thermal insulation area7A is thus provided, whereby the insulation properties between theflexible area2 and the movingelement5 are enhanced and heat generated by a diffusedresistor6 is prevented from escaping to the movingelement5 for efficiently heating theflexible area2, thereby decreasing power consumption.
• The rigidity of a[0232]thermal insulation area7 provided between asemiconductor substrate3 and theflexible area2 is made different from that of thethermal insulation area7A provided between theflexible area2 and the movingelement5 for determining the displacement direction of the movingelement5. For example, the rigidity of thethermal insulation area7 is made higher than that of thethermal insulation area7A, whereby the movingelement5 can be displaced downward in the thickness direction of the semiconductor substrate3 (downward in FIG. 11); the rigidity of thethermal insulation area7 is made lower than that of thethermal insulation area7A, whereby the movingelement5 can be displaced to an opposite side.
• In the embodiment, a round for easing a stress applied when the[0233]flexible area2 is displaced is provided in the proximity of the joint part of theflexible area2 and thesemiconductor substrate3 or the joint part of theflexible area2 and the movingpart5.
• That is, as shown in FIG. 12B, a[0234]projection part25 projecting inward roughly from the center of each side of thesemiconductor substrate3 which becomes a frame and theflexible area2 are joined by thethermal insulation area7, and a round25ais formed so that the shape on the substrate face on thesemiconductor substrate3 becomes like R at both ends of the base end part of theprojection part25. A mask is formed and wet etching, etc., is executed, thereby forming therounds25a.
• As shown in FIG. 12A, a[0235]recess part27 is made from the lower face side of thesemiconductor substrate3 in the figure and athin portion2S forming a part of theflexible area2 is formed in abottom face part27aof therecess part27, and around28 is formed so as to become shaped like R on the boundary between thebottom face part27aand aflank part27bof therecess part27. Therecess part27 is made by etching from the substrate face of the semiconductor substrate. For example, a sacrificial layer is formed on the boundary between thebottom face part27aand theflank part27bof therecess part27 and is removed by etching, whereby isotropy when the sacrificial layer is diffused is used to form theround28.
• The[0236]rounds25aand28 are thus formed, whereby the stress applied when theflexible area2 is displaced is scattered and eased by means of therounds25aand28, preventing thesemiconductor substrate3 from being destroyed. That is, if both base end part ends of theprojection part25 projecting inward from thesemiconductor substrate3 have an edge, there is a possibility that the stress of theflexible area2 will concentrate on the edge, breaking thesemiconductor substrate3. Likewise, if the boundary between thebottom face part27aand theflank part27bof therecess part27 provided for forming theflexible area2 has an edge, there is a possibility that the stress of theflexible area2 will concentrate on the edge, breaking thesemiconductor substrate3.
• FIG. 13 shows another structure example of the semiconductor microactuator formed with the thermal insulation areas between the flexible area and the semiconductor substrate and between the flexible area and the moving element as shown in FIGS. 11 and 12, and a manufacturing method therefor will be discussed.[0237]
• As shown in FIG. 13, a[0238]semiconductor substrate3aand aflexible area2aare joined via athermal insulation area7aand theflexible area2aand a movingelement5aare joined via athermal insulation area7b. Theflexible area2ais made up of athin film2mand a thin portion2sdifferent in thermal expansion coefficient, and a diffusedresistor6ais placed on a surface of the thin portion2s.Wiring13afor supplying power to the diffusedresistor6ais connected to the diffusedresistor6athrough the bottom face of thethermal insulation area7afrom an electrode pad (not shown) on thesemiconductor substrate3a.Numerals9aand9bdenote protective thin films.
• A manufacturing method of the semiconductor microactuator will be discussed with reference to FIGS. 14A to[0239]14E. First, asilicon oxide film80ais formed on both faces of amonocrystalline silicon substrate80 by thermal oxidation, etc., and thesilicon oxide film80aformed on the rear face of themonocrystalline silicon substrate80 is etched with a photoresist patterned to a predetermined pattern as a mask, thereby forming anopening80b, and the photoresist is removed by plasma ashing, etc. The formedopening80bis etched in aqueous potassium hydroxide (aqueous KOH), etc., thereby forming agap80c(FIG. 14A). At this time, TMAH (tetramethyl ammonium hydroxide solution), a hydrazine water solution, etc., may be used in place of the aqueous KOH. This also applies in the description to follow.
• Next, the[0240]silicon oxide film80ais fully removed, then boron, etc., is deposited and thermally diffused and diffusedresistors6aas heaters are formed on the surface of themonocrystalline silicon substrate80. Subsequently, asilicon oxide film81bis formed on both faces of themonocrystalline silicon substrate80 by thermal oxidation, etc., and asilicon nitride film81ais formed on the top of eachsilicon oxide film81bby low-pressure CVD (chemical vapor deposition) (FIG. 14B).
• The[0241]silicon oxide films81band thesilicon nitride film81aare etched with photoresists patterned to predetermined patterns as masks, thereby formingopenings82, and the photoresists are removed by plasma ashing, etc., (FIG. 14C).
• Next, the[0242]openings82 in themonocrystalline semiconductor substrate80 are etched in aqueous KOH, etc., thereby forming a movingelement5aand thin portions2s. At this time, to provide the movingelement5awith any desired thickness and each thin portion2swith any desired thickness, etching from each face of themonocrystalline semiconductor substrate80 may be started at different timing. Then, themonocrystalline semiconductor substrate80 is etched, thereby forminggrooves83aand83bto formthermal insulation areas7aand7b. Thegrooves83aand83bare grooves to be filled with an organic material of polyimide, etc., at a later step, and etching is performed so that the bottom thickness of each groove becomes about 10 μm (FIG. 14D).
• Subsequently, the substrate surface etched to form the moving[0243]element5aand the thin portions2sis oxidized for formingprotective films84 required when the substrate is plated (FIG. 14E).
• Aluminum is put on the top face of the[0244]monocrystalline semiconductor substrate80 by sputtering or EB evaporation and wiring13a(aluminum wiring) connected to the diffusedresistors6ais formed (FIG. 15A).
• Next, the[0245]grooves83aand83bare filled with anorganic substance85 of polyimide, etc., (FIG. 15B). Thus, a structure wherein thewiring13ais formed on the lower faces of theorganic substances85 is provided. Theorganic substances85 of polyimide, etc., are formed only in predetermined portions using a semiconductor lithography process.
• Next, a metal pattern of a predetermined pattern is formed on the[0246]silicon nitride film81a(the protectivethin film9ain FIG. 13) above the thin portions2sby plating, etc., to formthin films2m(FIG. 15C). The thin portions2sand thethin films2mmake up a bimetal structure of a drive source of the semiconductor microactuator.
• Next, etching is performed by RIE, etc., from the rear faces of the thin portions[0247]2sand the thin portions2sare separated from the periphery of the monocrystalline semiconductor substrate80 (thesemiconductor substrate3ain FIG. 13) and the movingelement5a(FIG. 15D), whereby the movingelement5a, theflexible areas2a, and thesemiconductor substrate3aare thermally insulated and thethermal insulation area7a,7bis provided therebetween.
• By the way, in the structure example shown in FIG. 13, the[0248]wiring13ais placed on the lower part face of thethermal insulation area7a, but wiring (aluminum wiring)13bmay be placed roughly in the middle of the top and bottom faces of eachthermal insulation area7a, namely, in thethermal insulation areas7a, as shown in FIG. 16.
• To thus form the[0249]wiring13b, after the formation step of theprotective film84 shown in FIG. 14E, thegrooves83aformed at the step in FIG. 14D may be filled with polyimide roughly to the centers at the step of filling with theorganic substance85 of polyimide, etc., shown in FIG. 15B, the wiring formation step shown in FIG. 15A may be performed, and thegrooves83amay be filled by again executing the filling step shown in FIG. 15B.
• Since the[0250]wiring13bis thus formed in thethermal insulation areas7a, the aluminum protection effect at an etching step, etc., of later steps, is produced and a high-reliability wiring structure can be provided.
• In the above-described wiring structure, the wiring may be placed on the top faces of the thermal insulation areas (FIG. 12A); the wiring is formed on the face on the side where the flexible areas, the thermal insulation areas, and the semiconductor substrate flush with each other, so that the wiring level difference is lessened and the line break prevention effect is produced as compared with the case where the wiring is placed in the thermal insulation areas or on the bottom faces thereof.[0251]
• To thus form the wiring on the top faces of the thermal insulation areas, after the formation step of the[0252]protective film84 shown in FIG. 14E, thegrooves83aformed at the step in FIG. 14D may be filled with polyimide at the step of filling with theorganic substance85 of polyimide, etc., shown in FIG. 15B, then the wiring may be formed on the top face of polyimide at the wiring formation step shown in FIG. 15A.
• Third Embodiment[0253]
• Next, a third embodiment of the invention will be discussed. FIGS. 17 and 18 are a perspective view and a top view to show the structure of a semiconductor microactuator in the third embodiment of the invention. A semiconductor microactuator in the third embodiment differs from that in the second embodiment in that the[0254]wiring4afor supplying power to the diffusedresistors6 is connected to the diffusedresistors6 through the tops of thethermal insulation areas7 in the second embodiment; whereas, in the third embodiment, afillet part29 made of an organic material, for example, is formed in a part extending over asemiconductor substrate3 and athin portion2S of a flexible area2 (so-called inlet corner) andwiring4ais formed through thefillet parts29. That is, in the embodiment, thewiring4ais formed without the intervention ofthermal insulation areas7.
• This structure can be manufactured by the following method: A groove is formed from the side of the top face of the semiconductor substrate where[0255]flexible areas2 are formed, for example, by anisotropic etching, a resin of an organic material, such as polyimide, is poured into the groove and is cured at a high temperature, and etching is performed for removal until thefillet parts29 appear from the rear face of the semiconductor substrate, then thewiring4ais formed on the top faces of thefillet parts29 by sputtering, etc., aluminum.
• The[0256]wiring4ais made of a material having very good thermal conductivity, such as aluminum, and thus may be heat resistance of a fraction of that ofthermal insulation area7 made of a resin although it has a small cross-sectional area. If thewiring4ais formed in thethermal insulation areas7, the thermal insulation distance of thewiring4acannot be provided and consequently the thermal insulation performance of thethermal insulation areas7 cannot be provided. In the embodiment, thewiring4ais formed without the intervention of thethermal insulation areas7, so that a large thermal insulation distance of thewiring4acan be provided and the thermal insulation effect can be enhanced with heat resistance degradation suppressed. The mechanical strength of thethermal insulation areas7 is increased as thefillet parts29 are formed.
• Thus, with the semiconductor microactuator in the embodiment, the thermal insulation effect is enhanced and further low power consumption is enabled as compared with the semiconductor microactuator in the second embodiment.[0257]
• Fourth Embodiment[0258]
• Next, a fourth embodiment of the invention will be discussed. FIGS. 19 and 20 are a perspective view and a top view to show the structure of a semiconductor microactuator in the fourth embodiment of the invention. A[0259]semiconductor microactuator31 in the fourth embodiment differs from the semiconductor microactuator in the first embodiment in that the fourthin portions2S each shaped roughly like a quadrangle piece, of theflexible areas2 are roughly in the shape of a cross with the movingelement5 at the center in the first embodiment; whereas, in thesemiconductor microactuator31 of the fourth embodiment, fourthin portions32S offlexible areas32 are each shaped roughly like L, eachthin portion32S is connected at one end roughly to the center of each side of the top face margin opened like a quadrangle, of a movingelement35, and theflexible areas32 are shaped like the Buddhist cross with the movingelement35 at the center. That is, thethin portions32S of theflexible areas32 are placed at equal intervals in every direction with the movingelement35 at the center. Further, eachthin portion32S is joined at an opposite end to the end of each side of asemiconductor substrate33 of a quadrangular frame via athermal insulation area37.
• Each[0260]flexible area32 is made up of thethin portion32S and athin film32M made of aluminum, nickel, etc., like the flexible area in the first embodiment, and each diffusedresistor36 of heating means is formed on the surface of thethin portion32S as in the first embodiment. External power is supplied to the diffusedresistors36 viaelectrode pads34 placed at the four corners of thesemiconductor substrate33 andwiring34a. Thesemiconductor substrate33, theflexible areas32, and thethermal insulation area37 make up asemiconductor device38.
• In the[0261]semiconductor microactuator31, like the semiconductor microactuator of the first embodiment, as the temperatures of the diffusedresistors36 rise, theflexible areas32 are heated and are displaced downward because of the thermal expansion difference between eachthin portion32S and eachthin film32M (if thethin film32M has a larger thermal expansion coefficient than thethin portion32S). Theflexible areas32 are displaced downward, whereby the movingelement35 joined to theflexible areas32 receives the thermal stress of theflexible areas32 and is displaced downward with respect to thesemiconductor substrate33.
• In the embodiment, the[0262]flexible areas32 are shaped like the Buddhist cross with the movingelement35 at the center as described above, thus the displacement of the movingelement35 contains rotation in the horizontal direction with respect to thesemiconductor substrate33. Since eachflexible area32 is shaped like L, the length of theflexible area32 can be made long as compared with the case where theflexible area32 is shaped simply like a quadrangle piece, and the displacement of theflexible area32 becomes large, so that displacement of the movingelement35 can be made large. Thesemiconductor device38 may adopt any of the structures shown in FIGS. 3, 6, and9, and a semiconductor microactuator having similar advantages to those of the semiconductor microactuators described above can be provided.
• Fifth Embodiment[0263]
• Next, a fifth embodiment of the invention will be discussed. FIGS. 21 and 22 are a perspective view and a top view to show the structure of a semiconductor microactuator of the fifth embodiment of the invention. A[0264]semiconductor microactuator31aof the embodiment also includesflexible areas32 shaped like the Buddhist cross with a movingelement35 at the center and hasthermal expansion areas37aeach placed between the movingelement35 and eachflexible area32 for joining the movingelement35 and theflexible areas32.
• The[0265]thermal expansion areas37athus provided, whereby the heat insulation properties between theflexible areas32 and the movingelement35 is enhanced and the heat generated by diffusedresistors36 can be prevented from escaping to the movingelement35. Therefore, theflexible areas32 can be heated efficiently for decreasing power consumption as compared with the fourth embodiment.
• In the embodiment, a round for easing a stress applied when the[0266]flexible area32 is displaced is provided in the proximity of the joint part of theflexible area32 and asemiconductor substrate33 or the joint part of theflexible area32 and the movingpart5 as in the embodiment previously described with reference to FIGS. 11 and 12. For example, as shown in FIG. 22A, a round39ashaped like R is formed at both base end part ends of aprojection part39 projecting inward from each side end part of thesemiconductor substrate33.
• Sixth Embodiment[0267]
• Next, a sixth embodiment of the invention will be discussed. FIG. 23 is a perspective view to show the structure of a semiconductor microactuator of the sixth embodiment of the invention. A[0268]semiconductor microactuator41 of the embodiment includes asemiconductor substrate43 which becomes a hollow frame shaped roughly like a quadrangle, fourthin portions42S each shaped roughly like a quadrangle piece, thethin portions42S separated from thesemiconductor substrate43 with one ends joined viathermal insulation areas47 inwardly from the sides of thesemiconductor substrate43, a movingelement45 formed like a hollow quadrangular prismoid with the top face opened like a quadrangle and narrower toward the bottom, the movingelement45 having top opening margins connected to opposite ends of thethin portions42S, andthin films42M of aluminum thin films, nickel thin films, or the like placed on the top faces of thethin portions42S, eachthin film42M and eachthin portion42S making up aflexible area42.
• The[0269]semiconductor substrate43, thethin portions42S, and the movingelement45 are formed, for example, by working a semiconductor substrate of a silicon substrate, etc. Eachthin portion42S is formed on a surface with an impurity-diffused resistor46 (diffused resistor46) of heating means. Power is supplied to the diffusedresistors46 by wiring44aconnected toelectrode pads44 placed on thesemiconductor substrate43 and connected to an external power supply, and the temperatures of the diffusedresistors46 rise, heating theflexible areas42. Thethin film42M is made of aluminum, nickel, or the like as described above and thethin portion42S is made of silicon, etc.; thethin film42M and thethin portion42S have different thermal expansion coefficients.
• Each[0270]thermal insulation area47 for joining thesemiconductor substrate43 and theflexible area42 has roughly the same thickness as thethin portion42S and is made of a thermal insulation material such as a fluoridated resin or polyimide for thermally insulating thesemiconductor substrate43 and theflexible area42. Thesemiconductor substrate43, theflexible areas42, and thethermal insulation areas47 each between thesemiconductor substrate43 and theflexible area42 make up asemiconductor device48. Thesemiconductor microactuator41 has a cantilever structure with eachflexible area42 supported at one end on thesemiconductor substrate43.
• In the[0271]semiconductor microactuator41, upon application of power to the diffusedresistors46, the temperature rises, heating theflexible areas42, and a thermal stress occurs because of the difference between the thermal expansion coefficients of thethin film42M and thethin portion42S making up eachflexible area42. For example, if metal thin films of aluminum, nickel, etc., are formed as thethin films42M, the metal of aluminum, nickel, etc., has a lager thermal expansion coefficient than silicon forming thethin portions42S, so that theflexible areas42 are bent downward in the figure. The movingelement45 placed contiguous with theflexible areas42 receives the thermal stress of theflexible areas42 and is displaced downward with respect to thesemiconductor substrate43.
• In the embodiment, the[0272]flexible areas42 are of cantilever structure, so that large flexibility of theflexible areas42 can be provided and displacement of theflexible areas42 at the heating time becomes large. Thus, displacement of the movingelement45 becomes large and a large force is provided. Thesemiconductor device48 may adopt any of the structures previously described with reference to FIGS. 3, 6, and9 in the first embodiment, and a semiconductor microactuator having similar advantages to those of the semiconductor microactuators described above can be provided.
• Seventh Embodiment[0273]
• Next, a seventh embodiment of the invention will be discussed. FIG. 24 is a perspective view to show the structure of a[0274]semiconductor microactuator41aof the seventh embodiment of the invention. The seventh embodiment differs from the sixth embodiment in that eachflexible area42 and a movingelement45 are joined by athermal insulation area47amade of a resin such as polyimide or a fluoridated resin, thethermal insulation area47abeing placed between theflexible area42 and the movingelement45.
• The new[0275]thermal insulation area47ais thus provided, whereby the insulation properties between theflexible area42 and the movingelement45 are enhanced and heat generated by a diffusedresistor46 can be prevented from escaping to the movingelement45; theflexible areas42 can be heated efficiently for decreasing power consumption as compared with the sixth embodiment.
• Eighth Embodiment[0276]
• Next, an eighth embodiment of the invention will be discussed. FIG. 25 is a perspective view to show the structure of a[0277]semiconductor microactuator41bof the eighth embodiment of the invention. The eighth embodiment differs from the seventh embodiment in that athin film47M of aflexible area42 and athermal insulation area47 are made of the same material, a resin having thermal insulation properties, such as polyimide or a fluoridated resin, whereby it is made possible to form thethermal insulation area47 and thethin film47M at the same time; the manufacturing process can be simplified.
• A moving[0278]element45 of thesemiconductor microactuator41bis formed with aconcave part45H as a groove made from the top face. The heat capacity of the movingelement45 lessens as compared with a movingelement45aof asemiconductor microactuator41cshown in FIG. 26 (the movingelement45aformed with no concave part), so that the temperatures of theflexible areas42 can be raised rapidly. Theconcave part45H is formed, whereby the weight (volume) of the moving element lessens, so that thesemiconductor microactuator41balso has the advantage that it does not malfunction upon reception of an external shock.
• Ninth Embodiment[0279]
• Next, a ninth embodiment of the invention will be discussed. FIG. 27 is a partially cutaway view in perspective of the structure of a semiconductor microvalve[0280]55 in the ninth embodiment of the invention. The semiconductor microvalve55 includes apedestal50 of a fluid element formed by working a substrate and an actuator section joined onto the top of thepedestal50 by anodic junction or eutectic junction. Thesemiconductor microactuator1 comprising theflexible areas2 in the shape of a cross with the movingelement5 at the center previously described with reference to FIGS. 1 and 2 is used as the actuator section.
• The[0281]pedestal50 is formed with a through hole51 (so-called orifice) corresponding to a fluid flow passage at the position corresponding to the movingelement5 of thesemiconductor microactuator1 placed on the surface of thepedestal50, and abed part52 with a roughly flat top face, projecting from the surroundings is formed in the periphery of a top face opening of the throughhole51. The movingelement5 corresponds to a so-called valve body.
• In the described semiconductor microvalve[0282]55, when power is supplied to the diffusedresistors6 for heating theflexible areas2, eachflexible area2 is displaced because of the thermal expansion difference between thethin portion2S and thethin film2M and the movingelement5 joined to theflexible areas2 is displaced. As the movingelement5 is displaced, the spacing between the bottom face part of the movingelement5 and thebed part52 of thepedestal51 changes, controlling the quantity of the fluid flowing through the throughhole51.
• The semiconductor microvalve[0283]55 of the embodiment is also formed with thethermal insulation area7 made of a resin of polyimide, etc., between thesemiconductor substrate3 and eachflexible area2, so that the heat for heating theflexible areas2 can be prevented from escaping to thesemiconductor substrate3. Thus, it is made possible to suppress power consumption in driving the semiconductor microvalve.
• Since the four[0284]flexible areas2 are in the shape of a cross with the movingelement5 at the center, the semiconductor microvalve is provided with good control accuracy of the movingelement5 and fluid.
• FIG. 28 shows a configuration example of using the[0285]semiconductor microactuator1apreviously described with reference to FIGS. 11 and 12 as the actuator section of the semiconductor microvalve in FIG. 27. The semiconductor microvalve in FIG. 28 includes thepedestal50 and thesemiconductor microactuator1ajoined via spacer layers53 made of polyimide.
• The[0286]thermal insulation area7A is also provided between eachflexible area2 and the movingelement5, so that it is made possible to more lessen the escape heat from theflexible areas2 as compared with the semiconductor microvalve shown in FIG. 27, and power consumption in driving the semiconductor microvalve can be suppressed.
• The advantage provided by providing rounds each for easing a stress applied when the[0287]flexible area2 is displaced in the joint part of theflexible area2 and thesemiconductor substrate3 or in the proximity of the joint part of theflexible area2 and the movingpart5 is similar to that previously described with reference to FIGS. 11 and 12.
• Further, the spacer layers[0288]53 are formed between thepedestal50 and thesemiconductor microactuator1a, whereby the following advantage is provided: Normally, thesemiconductor microactuator1ais made of a silicon substrate and thepedestal50 is made of a glass substrate. Since both are joined under a high temperature (anodically joined at 400° C.), a stress occurs therebetween at a room temperature because of the shrinkage degree difference caused by the thermal expansion difference between the silicon and glass substrates. Since the stress concentrates on theflexible areas2 of thesemiconductor microactuator1a, sufficient displacement of theflexible areas2 cannot be provided and the drivability of the semiconductor microvalve worsens. Then, the spacer layers53 are provided between thepedestal50 and thesemiconductor microactuator1a, whereby the stress occurring therebetween can be absorbed and eased as described above.
• The operation of the semiconductor microvalve in FIG. 28 is similar to that of the semiconductor microvalve in FIG. 27 and therefore will not be discussed again.[0289]
• FIG. 29 shows a configuration example of using the[0290]semiconductor microactuator1bpreviously described with reference to FIG. 17 as the actuator section of the semiconductor microvalve in FIG. 27. The semiconductor microvalve in FIG. 29 differs from that shown in FIG. 28 in that thewiring4afor supplying power to the diffusedresistors6 for heating theflexible areas2 is formed without the intervention of thethermal insulation areas7. Since it is made possible to provide a large thermal insulation distance of thewiring4a, the semiconductor microvalve can be provided with a higher thermal insulation effect and power consumption for driving the semiconductor microvalve can be suppressed.
• The operation of the semiconductor microvalve in FIG. 29 is similar to that of the semiconductor microvalve in FIG. 27 and therefore will not be discussed again.[0291]
• Tenth Embodiment[0292]
• Next, a tenth embodiment of the invention will be discussed. FIG. 30 is a partially cutaway view in perspective of the structure of a semiconductor microvalve in the tenth embodiment of the invention. The semiconductor microvalve includes a[0293]pedestal56 of a fluid element formed by working a substrate and an actuator section joined onto the top of thepedestal56 by anodic junction or eutectic junction. Thesemiconductor microactuator31 comprising theflexible areas32 shaped like the Buddhist cross with the movingelement35 at the center previously described with reference to FIGS. 19 and 20 is used as the actuator section.
• The[0294]pedestal56 is formed with a through hole57 (so-called orifice) corresponding to a fluid flow passage at the position corresponding to the movingelement35 of thesemiconductor microactuator31 placed on the surface of thepedestal56, and abed part58 with a roughly flat top face, projecting from the surroundings is formed in the periphery of a top face opening of the throughhole57. The movingelement35 corresponds to a so-called valve body. In the described semiconductor microvalve, when power is supplied to the diffusedresistors36 for heating theflexible areas32, eachflexible area32 is displaced because of the thermal expansion difference between thethin portion32S and thethin film32M and the movingelement35 joined to theflexible areas32 is displaced. As the movingelement35 is displaced, the spacing between the bottom face part of the movingelement35 and thebed part58 of thepedestal56 changes, controlling the quantity of the fluid flowing through the throughhole57.
• The semiconductor microvalve of the embodiment is also formed with the[0295]thermal insulation area37 made of a resin of polyimide, etc., between thesemiconductor substrate33 and eachflexible area32, so that the heat for heating theflexible areas32 can be prevented from escaping to thesemiconductor substrate33. Thus, it is made possible to suppress power consumption in driving the semiconductor microvalve.
• Since the semiconductor microvalve of the embodiment includes the[0296]flexible areas32 each shaped like L, the length of each flexible area is long, so that displacement of theflexible areas32 becomes large, thus displacement of the movingelement35 can be made large. Therefore, the semiconductor microvalve is provided with a wide range of fluid flow quantity control.
• FIG. 31 shows a configuration example of using the[0297]semiconductor microactuator31apreviously described with reference to FIGS. 21 and 22 as the actuator section in FIG. 30. The semiconductor microvalve in FIG. 31 also includes thethermal insulation area37aprovided between eachflexible area32 and the movingelement35, so that it is made possible to more lessen the escape heat from theflexible areas32 as compared with the semiconductor microvalve shown in FIG. 30, and power consumption in driving the semiconductor microvalve can be suppressed.
• The advantage provided by providing rounds each for easing a stress applied when the[0298]flexible area32 is displaced in the proximity of the joint part of theflexible area32 and thesemiconductor substrate33 or the joint part of theflexible area32 and the movingpart35 is similar to that previously described with reference to FIGS. 21 and 22.
• Eleventh Embodiment[0299]
• Next, an eleventh embodiment of the invention will be discussed. FIG. 32 is a partially cutaway view in perspective of the structure of a semiconductor microrelay in the eleventh embodiment of the invention. The semiconductor microrelay in FIG. 32 includes a fixed[0300]piece65 of a fixed element formed on a surface with fixedcontacts67 and68 and an actuator section joined onto the top of the fixedpiece65 by anodic junction or eutectic junction. Thesemiconductor microactuator41 previously described with reference to FIG. 23 is used as the actuator section.
• A moving[0301]contact66 is provided on the bottom face of the movingelement45 of thesemiconductor microactuator41, and the fixedcontacts67 and68 on the fixedpiece65 are placed at the positions corresponding to the movingcontact66 away therefrom so that they can come in contact with the movingcontact66.
• When an electric current flows into the diffused[0302]resistors46 and theflexible areas42 are heated, eachflexible area42 is displaced because of the thermal expansion difference between thethin portion42S and thethin film42M and the movingelement45 is displaced. As the movingelement45 is displaced, the movingcontact66 provided on the bottom face of the movingelement45 comes in contact with the fixedcontacts67 and68, and the fixedcontacts67 and68 are brought into conduction through the fixedcontact66, turning on the relay.
• The actuator section of the semiconductor microrelay of the embodiment uses the[0303]semiconductor microactuator41; the semiconductor microrelay is provided with a high thermal insulation effect between theflexible areas42 and thesemiconductor substrate43 and small power consumption as described in the sixth embodiment. Thesemiconductor microactuator41 is of a cantilever structure with thesemiconductor substrate43 as a fixed end and the semiconductor microrelay is provided with a large contact pressure.
• Twelfth Embodiment[0304]
• Next a twelfth embodiment of the invention will be discussed. FIG. 33 is a perspective view to show the structure of a semiconductor microrelay in the twelfth embodiment of the invention. The actuator section shown in FIG. 32 uses the[0305]semiconductor microactuator41bpreviously described with reference to FIG. 25.
• That is, in the semiconductor microrelay of the embodiment, the[0306]thin films47M of theflexible areas42 and thethermal insulation areas47 for joining theflexible areas42 and thesemiconductor substrate43 are made of the same material, such as polyimide.
• In the semiconductor microrelay shown in FIG. 33, the moving[0307]element45 is formed with theconcave part45H. As compared with a moving element formed with no concave part shown in FIG. 37, the small heat capacity is small and the temperatures of theflexible areas42 can be raised rapidly, and the weight (volume) of the moving element lessens, thus the moving element does not malfunction upon reception of an external shock, as previously described with reference to FIG. 25.
• Next, a semiconductor microrelay manufacturing method in the embodiment will be discussed. A[0308]semiconductor substrate43, such as a silicon substrate, (see FIG. 34A) is etched for removal from the bottom face with KOH, etc., with a silicon nitride film, etc., as a mask, forming a gap40 (see FIG. 34B). Thegap40 becomes a contact gap between moving and fixed contacts in the semiconductor microrelay. Thesemiconductor substrate43 of a silicon substrate may be the p or n type and preferably the crystal orientation is <100>.
• Next, a diffused[0309]resistor46 is formed on the top face of thesemiconductor substrate43 by ion implantation or impurity diffusion (see FIG. 34C). The impurities may be the p or n type.
• Further, a silicon nitride film, etc., is formed on both faces of the[0310]semiconductor substrate43 and patterning is performed. Then, etching (anisotropic etching) is executed for removal with KOH, etc., from the top face of thesemiconductor substrate43 and aconcave part45H is formed on the top of a movingelement45 as a hollow shape. At the same time, etching (anisotropic etching) is executed for removal with KOH, etc., from the bottom face of thesemiconductor substrate43 to make a concave part, and the bottom face portion of the concave part is formed as athin portion42S forming a part of a flexible area (see FIG. 34D).
• Next, etching is executed for removal with a silicon nitride film, etc., as a mask from the top face of the[0311]semiconductor substrate43 to makeholes47B and47C in the portions which will becomethermal insulation areas47 and47a(see FIG. 35A). The etching depth corresponds to the thickness of thethermal insulation area47,47a.
• At the next step, an aluminum thin film is formed by sputtering, etc., and patterning is performed, whereby wiring[0312]49A for supplying power to the diffusedresistor46 and the like are formed (see FIG. 35B).
• Next, the full face of the[0313]semiconductor substrate43 is coated with a film of thermal insulation material of polyimide, etc., to fill in theholes47B and47C. Then, the thermal insulation material except that of the fill-in portions or that above thethin portion42S is removed by etching, etc., and thethermal insulation areas47 and47aand athin film47M are formed of the same material of polyimide, etc., (see FIG. 35C). The bottom face sides of thethermal insulation areas47 and47aare etched for removal (see FIG. 35D) and the movingelement45 is formed on the bottom face side with a moving contact66 (described later) made of gold cobalt, etc., by plating, etc., (see FIG. 35E).
• Then, the[0314]semiconductor substrate43 thus worked and a fixedpiece65 formed with a fixedcontact67 of gold cobalt, etc., by plating are joined by anodic junction, etc., (see FIG. 36A). Last, the movingelement45 and theflexible area42 are separated from thesemiconductor substrate43 which becomes a frame by RIE, etc., for manufacturing a semiconductor microrelay (see FIG. 36B). That is, thesemiconductor microactuator41bis manufactured.
• Since the[0315]thin film47M of theflexible area42 and thethermal insulation area47 are thus formed of the same material at the same time, so that the manufacturing process is simplified and the costs can be reduced.
• FIG. 38 shows a so-called bimetal structure consisting of the[0316]thin portion42S and thethin film47M of theflexible area42 in the semiconductor microrelay of the embodiment. As shown in the figure, polyimide (trade name “Photonis”)20 um thick as thethin film47M is formed on the top of thethin portion42S made ofsilicon 10 μm thick. Theflexible area42 has plane dimensions of 1000 μm×1000 μm. At this time, the bend of theflexible area42 is represented by the following Timochenko's expression:$\begin{array}{cc}\begin{array}{c}\frac{1}{\rho }=\frac{6\left({\alpha }_{\mathrm{Si}}-{\alpha }_{\mathrm{ph}}\right)\Delta T\left(t_{\mathrm{Si}}+t_{\mathrm{ph}}\right)t_{\mathrm{Si}}·t_{\mathrm{ph}}·E_{\mathrm{Si}}·{\mathrm{<figure-callout\; label="E\; ph"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathrm{ph}}}{3{\left(t_{\mathrm{Si}}+t_{\mathrm{ph}}\right)}^2t_{\mathrm{Si}}t_{\mathrm{ph}}E_{\mathrm{Si}}E_{\mathrm{ph}}+\left(t_{\mathrm{Si}}E_{\mathrm{Si}}+t_{\mathrm{ph}}E_{\mathrm{ph}}\right)\left({\mathrm{<figure-callout\; label="t\; Si"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{Si}}^{}E_{\mathrm{Si}}+{\mathrm{<figure-callout\; label="t\; ph"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{ph}}^{}E_{\mathrm{ph}}\right)}\\ w=2\rho {\mathrm{<figure-callout\; label="sin"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\left(\frac{\mathrm{<figure-callout\; label="L"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">L</figure-callout>}}{2\rho }\right);\frac{\mathrm{<figure-callout\; label="L"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">L</figure-callout>}}{2\rho }\left[\mathrm{rad}\right]\mathrm{in}\left[\mathrm{rad}\right]\mathrm{units}\end{array}& \left[\mathrm{Expression}16\right]\end{array}$

  
• where[0317]
• p; Curvature W; Displacement[0318]
• E[0319]_ph: Young's modulus of Photonis 490×10⁹N/m²
• E[0320]_si: Young's modulus of silicon 1.90×10¹¹N/m²
• α[0321]_ph: Linear expansion coefficient 2.30×10⁻⁵/K of Photonis
• α[0322]_si: Linear expansion coefficient 4.15×10⁻⁶/K of silicon
• t[0323]_ph: Thickness ofPhotonis 20 μm
• t[0324]_si: Thickness ofsilicon 10 μm
• where ΔT denotes temperature change.[0325]
• FIG. 39 shows the calculation result of the expression to which specific numeric values are assigned. As shown in FIG. 39, the higher the temperature of the[0326]flexible area42, the larger the displacement (bend) of theflexible area42. If the bend becomes larger than the contact gap between the movingcontact66 and the fixedcontact67,68 of the semiconductor microrelay, the movingcontact66 comes in contact with the fixedcontacts67 and68, turning on the relay.
• The bimetal operation when the contact gap is 20 μm and the bimetal is at 200° C. will be discussed. As shown in FIG. 39, displacement of the bimetal at 200° C. is about 65 μm.[0327]
• The semiconductor microrelay is of a cantilever structure and the beam corresponding to the[0328]flexible area42 is displaced as shown in FIG. 40. Displacement of the tip, Xa, is represented as Xa=(Fa τa³)/(3Ea Ia). Fa denotes the force applied to the tip of the beam, ta denotes the thickness of the beam, τa denotes the length of the beam, and Ea denotes the Young's modulus of the beam. Ia denotes the secondary moment of the cross section of the beam. If the beam is rectangular in cross section, Ia=ba ta³/12 (where ba denotes the deep width of the beam), thus the bend of the tip, Xa,=4 Fa τa³/(ba ta³Ea). According to this expression, the force applied to the tip of the beam, Fa, is represented as Fa=(Xa ba ta³Ea)/(4 τa³). Letting the contact gap be 20 μm, contact pressure fa becomes equal to ((Xa−20 μm) ba ta³Ea)/(4 τa³). Since the bend of the tip, Xa, is 65 μm, the contact pressure fa becomes equal to 0.87 gf=8.5×10⁻³N; the contact pressure almost close to 1 gf (9.8×10⁻³N) is provided.
• Thirteenth Embodiment[0329]
• Next, a thirteenth embodiment of the invention will be discussed. FIG. 41 is a perspective view to show the structure of a semiconductor microrelay of the thirteenth embodiment of the invention. The semiconductor microrelay shown in FIG. 41 includes the[0330]semiconductor microactuator41 previously described with reference to FIG. 23 as the actuator section of the semiconductor microrelay shown in FIG. 33. The semiconductor microrelay of the embodiment differs from the semiconductor microrelay in FIG. 33 in that thethin film42M of eachflexible area42 is made of a metal thin film such as an aluminum or nickel thin film.
• Also in the semiconductor microrelay of the embodiment, the moving[0331]element45 is formed with theconcave part45H; as compared with a semiconductor microrelay shown in FIG. 48 with a moving element formed with no concave part, the temperatures of theflexible areas42 can be raised rapidly, and the weight (volume) of the moving element lessens, thus malfunction can be prevented upon reception of an external shock, as in the twelfth embodiment.
• Next, manufacturing methods of the semiconductor microrelay shown in FIG. 41 will be discussed. First, a manufacturing method of the semiconductor microrelay wherein the[0332]thin film42M forming a part of eachflexible area42 is made of an aluminum thin film will be discussed.
• A[0333]semiconductor substrate43, such as a silicon substrate, (see FIG. 42A) is etched for removal from the bottom face with KOH, etc., with a silicon nitride film, etc., as a mask, forming a gap40 (see FIG. 42B). Thegap40 becomes a contact gap between moving and fixed contacts in the semiconductor microrelay. The semiconductor substrate43 (silicon substrate) may be the p or n type and preferably the crystal orientation is <100>.
• Next, a diffused[0334]resistor46 is formed on the top face of thesemiconductor substrate43 by ion implantation or impurity diffusion (see FIG. 42C). The impurities may be the p or n type.
• Further, a silicon nitride film, etc., is formed on both faces of the[0335]semiconductor substrate43 and patterning is performed. Then, etching (anisotropic etching) is executed for removal with KOH, etc., from the top face of thesemiconductor substrate43 and aconcave part45H is formed on the top of a movingelement45 as a hollow shape. At the same time, etching (anisotropic etching) is executed for removal with KOH, etc., from the bottom face of thesemiconductor substrate43 to make a concave part, and the bottom face portion of the concave part is formed as athin portion42S forming a part of a flexible area (see FIG. 42D).
• Next, etching is executed for removal with a silicon nitride film, etc., as a mask from the top face of the[0336]semiconductor substrate43 to makeholes47B and47C in the portions which will becomethermal insulation areas47 and47a(see FIG. 43A). The etching depth corresponds to the thickness of thethermal insulation area47,47a.
• At the next step, an aluminum thin film is formed by sputtering, etc., and patterning is performed, whereby a[0337]thin film42M forming a part of a flexible area andwiring49A for supplying power to the diffusedresistor46 are formed, as shown in FIG. 43B. Then, the full face of thesemiconductor substrate43 is coated with a film of thermal insulation material of polyimide, etc., to fill in theholes47B and47C made in the top face of thesemiconductor substrate43, and the thermal insulation material other than the fill-in portions is removed by etching, etc., and thethermal insulation areas47 and47aare formed (see FIG. 43c).
• Then, the bottom face sides of the[0338]thermal insulation areas47 and47aare etched for removal for forming thethermal insulation areas47 and47athethermal insulation areas47 and47amade of only the thermal insulation material (see FIG. 43D). Next, the movingelement45 is formed on the bottom face side with a movingcontact66 made of gold cobalt, etc., by plating, etc.
• Next, the[0339]semiconductor substrate43 thus worked and a fixedpiece65 formed with a fixedcontact67 of gold cobalt, etc., by plating are joined by anodic junction, etc., (see FIG. 44A). Last, the movingelement45 and theflexible area42 are separated from thesemiconductor substrate43 which becomes a frame by RIE, etc., for manufacturing a semiconductor microrelay. That is, thesemiconductor microactuator41ais manufactured.
• Next, a manufacturing method of the semiconductor microrelay shown in FIG. 41 wherein the[0340]thin film42M is made of nickel will be discussed. As shown in FIGS. 45A to45E, the step of forming agap40 in the bottom face of asemiconductor substrate43, the step of forming a diffusedresistor46 in the top face of thesemiconductor substrate43, the step of forming aconcave part45H on the top of a movingelement45, the step of forming athin portion42S of aflexible area42, and the step of makingholes47B and47C of portions which will become thermal insulation areas are similar to the steps previously described with reference to FIGS. 42A to42D and43A and therefore will not be discussed again.
• At the next step, an aluminum thin film is formed by sputtering, etc., and patterning is performed, whereby wiring[0341]49A for supplying power to the diffusedresistor46 and the like are formed, as shown in FIG. 46A. Next, the full face of thesemiconductor substrate43 is coated with a film of thermal insulation material of polyimide, etc., to fill in theholes47B and47C made in the top face of thesemiconductor substrate43, the thermal insulation material other than the fill-in portions is removed by etching, etc., and thethermal insulation areas47 and47aare formed, as shown in FIG. 46B.
• Then, the bottom face sides of the[0342]thermal insulation areas47 and47aare etched for removal (see FIG. 46C), thethin portion42S is formed on the top face with a nickel thin film asthin film42M by plating, etc., (see FIG. 46D), and the movingelement45 is formed on the bottom face side with a movingcontact66 made of gold cobalt, etc., by plating, etc., (see FIG. 46E).
• Next, the[0343]semiconductor substrate43 thus worked and a fixedpiece65 formed with a fixedcontact67 of gold cobalt, etc., by plating are joined by anodic junction, etc., (see FIG. 47A). Last, the movingelement45 and theflexible area42 are separated from thesemiconductor substrate43 which becomes a frame by RIE, etc., for manufacturing a semiconductor microrelay (see FIG. 47B). That is, thesemiconductor microactuator41ais manufactured.
• FIG. 49 shows a so-called bimetal structure consisting of the[0344]thin portion42S and thethin film42M of theflexible area42 in the semiconductor microrelay shown in FIG. 41. As shown in FIG. 49, an aluminumthin film 5 μm thick as thethin film42M is formed on the top of thethin portion42S made ofsilicon 15 μm thick. Theflexible area42 has plane dimensions of 1000 μm×1000 μm.
• At this time, the displacement (bend) of the[0345]flexible area42 is represented by the following Timochenko's expression:$\begin{array}{cc}\begin{array}{c}\frac{1}{\rho }=\frac{6\left({\alpha }_{\mathrm{Si}}-{\alpha }_{\mathrm{Al}}\right)\Delta T\left(t_{\mathrm{Si}}+t_{\mathrm{Al}}\right)t_{\mathrm{Si}}·t_{\mathrm{Al}}·E_{\mathrm{Si}}·{\mathrm{<figure-callout\; label="E\; Al"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathrm{Al}}}{3{\left(t_{\mathrm{Si}}+t_{\mathrm{Al}}\right)}^2t_{\mathrm{Si}}t_{\mathrm{Al}}E_{\mathrm{Si}}E_{\mathrm{Al}}+\left(t_{\mathrm{Si}}E_{\mathrm{Si}}+t_{\mathrm{Al}}E_{\mathrm{Al}}\right)\left({\mathrm{<figure-callout\; label="t\; Si"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{Si}}^{}E_{\mathrm{Si}}+{\mathrm{<figure-callout\; label="t\; Al"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{Al}}^{}E_{\mathrm{Al}}\right)}\\ W=2\rho {\mathrm{<figure-callout\; label="sin"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\left(\frac{\mathrm{<figure-callout\; label="L"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">L</figure-callout>}}{2\rho }\right);\frac{\mathrm{<figure-callout\; label="L"\; filenames="US20030160538A1-20030828-D00000.png,US20030160538A1-20030828-D00001.png"\; state="\{\{state\}\}">L</figure-callout>}}{2\rho }\mathrm{in}\left[\mathrm{rad}\right]\mathrm{units}\end{array}& \left[\mathrm{Expresssion}17\right]\end{array}$

  
• where[0346]
• ρ; Curvature W; Displacement[0347]
• E[0348]_Al: Young's modulus of aluminum 6.86×10¹⁰N/m²
• E[0349]_si: Young's modulus of silicon 1.90×10¹¹N/m²
• α[0350]_Al: Linear expansion coefficient 2.37×10⁻⁵/K of aluminum
• α[0351]_si: Linear expansion coefficient 4.15×10⁻⁶/K of silicon
• t[0352]_Al: Thickness ofaluminum 5 μm
• t[0353]_si: Thickness of silicon
• where ΔT denotes temperature change.[0354]
• FIG. 50 shows the calculation result of the expression to which specific numeric values are assigned. As shown in FIG. 50, the higher the temperature of the[0355]flexible area42, the larger the displacement (bend) of theflexible area42. If the displacement becomes larger than the contact gap between the movingcontact66 and the fixedcontact67,68 of the semiconductor microrelay, the movingcontact66 comes in contact with the fixedcontacts67 and68, turning on the relay.
• The bimetal operation when the contact gap is 20 μm and the[0356]flexible area42 is at 200° C. will be discussed. As shown in FIG. 50, displacement of theflexible area42 at 200° C. is about 70 μm.
• The contact pressure fa is represented as fa=((Xa−20 μm) ba ta[0357]³Ea)/(4 τa³), as described above. If the contact pressure fa is found, fa=0.82 gf=8.0×10⁻³N; the contact pressure almost close to 1 gf (9.8×10⁻³N) is provided.
• On the other hand, to use a nickel thin film as the[0358]thin film42M, nickel has a smaller thermal expansion coefficient than aluminum, thus the displacement (bend) of theflexible area42 in response to temperature change is small. However, nickel has a larger Young's modulus than aluminum, so that a large thermal stress can be generated.
• FIG. 51 shows the displacement characteristics of the[0359]flexible area42 with thethin film42M made of aluminum and that with thethin film42M made of nickel as the thickness of thethin portion42S made of silicon is changed, wherein the aluminum film and the nickel film are each 5 μm thick and the temperature of theflexible area42 is 200° C. As seen in the figure, when thethin portion42S is 20 μm thick, the characteristics of theflexible area42 with aluminum and that with nickel are inverted and when thethin portion42S becomes more than 20 μm thick, the displacement characteristic of theflexible area42 with thethin film42M made of nickel becomes larger than that with thethin film42M made of aluminum. Thus, if thethin portion42S is thick, a good characteristic can be provided by using nickel as thethin film42M.
• FIG. 52 shows another configuration example of the semiconductor microrelay in the embodiment. The semiconductor microrelay in FIG. 52 differs from that in FIG. 41 in that it includes the fixed[0360]piece65 and thesemiconductor microactuator41ajoined via aspacer layer63 made of polyimide (for example, anodic junction). The stress occurring between the fixedpiece65 and thesemiconductor microactuator41acan be absorbed and eased, as in the embodiment previously described with reference to FIG. 28.
• FIGS. 57 and 58 show another configuration example of the semiconductor microactuator. FIG. 58([0361]a) is a sectional view and FIG. 58(b) is a top view. Asemiconductor microactuator7 shown in these figures is defined by thesemiconductor substrate3, made of the silicon or the like, which becomes a hollow parallelepiped shaped frame and a movingelement1, made of the silicon or the like, jointed at four portions through suspendingmeans4 from an inner side of the semiconductor substrate to suspend the movingelement1 from thesemiconductor substrate3.
• The moving[0362]element1 is shaped in a hollow truncated right pyramid in such a manner that quadrangle shaped portion is gradually reduced in an area along with a downwardly direction. Aboss2 is defined by the lower quadrangle portion of the truncated right pyramid. Theboss2 is suspended bycantilevered beam6 in such a manner that each cantilevered beam extends in a downwardly direction from one side of upper quadrangle of the truncated right pyramid. Eachcantilevered beam6 of four them serves as the extended leg portion of the crosswise through theboss2. The suspending means4 is made of polyimide, fluoridated resin or the like and is formed in such a manner that the surface of thesemiconductor substrate3 is jointed to the suspendingmeans4 contacted overlappingly to the upper side of the cantileveredbeam6 to join thesemiconductor substrate3 and the movingelement1. Thecantilevered beam6 is provided with heating means5, made of the diffusion resistor or the like, for heating the cantileveredbeam6.
• FIGS. 59 and 60 show another configuration example of the semiconductor microactuator. FIG. 59 is a partinally cut away view in perspective of the structure of a semiconductor microactuator using semiconductor device of the present invention. FIG. 60 is a top view. A[0363]semiconductor microactuator10 shown in these figures is defined by thesemiconductor substrate13, made of the silicon or the like, which becomes a hollow parallelepiped shaped frame and a movingelement11, made of the silicon or the like, jointed at four portions through suspendingmeans14 from an inner side of the semiconductor substrate to suspend the movingelement11 from thesemiconductor substrate13.
• The moving[0364]element11 is shaped in a hollow truncated right pyramid in such a manner that quadrangle shaped portion is gradually reduced in an area along with a downwardly direction. Aboss12 is defined by the lower quadrangle portion of the truncated right pyramid. Theboss12 is suspended bycantilevered beam16 in such a manner that each cantilevered beam extends in a downwardly direction from one side of upper quadrangle of the truncated right pyramid. Each cantileveredbeam16 of four them serves as the extended leg portion of the gammadion through theboss12. The suspending means4 is made of polyimide, fluoridated resin or the like and is formed in such a manner that the surface of thesemiconductor substrate13 is jointed to the suspending means14 contacted overlappingly to the upper side of the cantileveredbeam16 to join thesemiconductor substrate13 and the movingelement11.
• FIG. 61 shows another configuration example of the semiconductor microvalve, and is a partinally cut away view in perspective of the structure of a semiconductor microvalve using semiconductor device of the present invention. A[0365]semconductor microvalve30 is defined by avalve mount31 serving as a fluid control element and avalve body32 joined to the upper portion of thevalve mount31 through anodic junction or eutectic junction. This valve body employs the structure as same as the microactuator as shown in FIGS. 57 and 58.
• A[0366]orifice35 is provided on the surface of thevalve mount31 to be confronted with aboss2 of thevalve body32, and serves as a hole portion corresponding to the fluid flow path. Amount portion36 with an upper flat surface is formed by projecting a portion vicinity of theorifice35 to surround theorifice35.
• At that time, a current flows to the heating means[0367]5 to deform the beam of the movingelement1 so as to actuate the movingelement1. An actuation of the movingelement1 changes the gap defined by the bottom surface of theboss2 of thevalve body41 and themount portion36 to control a flow amount passing through theorifice35.
• FIG. 62 shows another configuration example of the semiconductor microvalve, and is a partinally cut away view in perspective of the structure of a semiconductor microvalve using semiconductor device of the present invention. A semconductor microvalve is defined by a[0368]valve mount41 serving as a fluid control element and avalve body42 joined to the upper portion of thevalve mount41 through anodic junction or eutectic junction. This valve body employs the structure as same as themicroactuator10 as shown in FIGS. 59 and 60.
• A[0369]orifice45 is provided on the surface of thevalve mount41 to be confronted with aboss12 of thevalve body42, and serves as a hole portion corresponding to the fluid flow path. Amount portion46 with an upper flat surface is formed by projecting a portion vicinity of theorifice45 to surround theorifice45.
• At that time, a current flows to the heating means (not shown in Figures) to deform the[0370]beam16 of the movingelement11 so as to actuate the movingelement11. An actuation of the movingelement1 changes the gap defined by the bottom surface of theboss12 of thevalve body41 and themount portion46 to control a flow amount passing through theorifice45.
• As described above, the semiconductor microactuator using the semiconductor device, the semiconductor microvalve, and the semiconductor microrelay in the related arts require large power consumption and thus it becomes difficult to drive them with a battery and it is made impossible to miniaturize them for portable use.[0371]
• It is therefore an object of the invention to provide a semiconductor device with small power consumption, manufactured by an easy manufacturing process, a semiconductor microactuator using the semiconductor device, a semiconductor microvalve, a semiconductor microrelay, and a semiconductor microactuator manufacturing method.[0372]
• [Means for Solving the Problem][0373]
• To the end, according to a first aspect of the present invention, there is provided a semiconductor device comprising a semiconductor substrate, a flexible area being isolated from the semiconductor substrate and displaced in response to temperature change, and a thermal insulation area being placed between the semiconductor substrate and the flexible area and made of a resin for joining the semiconductor substrate and the flexible area. The thermal insulation area made of a resin is placed between the semiconductor substrate and the flexible area, whereby heat escape when the temperature of the flexible area is changed is prevented, so that power consumption can be suppressed and further the manufacturing method is simple.[0374]
• In a second aspect to the present invention, in the semiconductor device as first aspect of the present invention, the material of which the thermal insulation area is made has a thermal conductivity coefficient of about 0.4 W/(m ° C.) or less. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced.[0375]
• In a third aspect of the present invention, in the semiconductor device as the second aspect of the present invention, the material of which the thermal insulation area is made is polyimide. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced and manufacturing the semiconductor device is facilitated.[0376]
• In a fourth aspect of the present invention, in the third aspect of the present invention, the material of which the thermal insulation area is made is a fluoridated resin. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced and manufacturing the semiconductor device is facilitated.[0377]
• In a fifth aspect of the present invention, in the first to fourth aspect of the present invention, a reinforcement layer made of a harder material than the material of which the thermal insulation area is made is provided on at least one face orthogonal to a thickness direction of the thermal insulation area. The joint strength of the semiconductor substrate and the flexible area can be increased.[0378]
• In a sixth aspect of the present invention, in the fifth aspect of the present invention, the reinforcement layer has a Young's modulus of 9.8×10[0379]⁹N/m²or more. The joint strength of the semiconductor substrate and the flexible area can be increased.
• In a seventh aspect of the present invention, in the sixth aspect of the present invention, the reinforcement layer is a silicon dioxide thin film. The joint strength of the semiconductor substrate and the flexible area can be increased.[0380]
• In an eighth aspect of the present invention, in the first to seventh aspect of the present invention, the portions of the semiconductor substrate and the flexible area in contact with the thermal insulation area form comb teeth. The joint strength of the semiconductor substrate and the flexible area can be increased.[0381]
• According to a ninth aspect of the present invention, there is provided a semiconductor device comprising a semiconductor device as the first to eighth aspect of the present invention and a moving element placed contiguous with the flexible area, wherein when temperature of the flexible area changes, the moving element is displaced relative to the semiconductor substrate. The semiconductor device which has similar advantages to those in the invention as claimed in[0382]claims 1 to 8 as well as can be driven with low power consumption can be provided.
• In a tenth aspect of the present invention, in the ninth aspect of the present invention, the flexible area has a cantilever structure. The semiconductor device can be provided with large displacement of the moving element.[0383]
• In an eleventh aspect of the present invention, in ninth aspect of the present invention, the moving element is supported by a plurality of flexible areas. The moving element can be supported stably.[0384]
• In a twelfth aspect of the present invention, in the eleventh aspect of the present invention, the flexible areas are in the shape of a cross with the moving element at the center. Good displacement accuracy of the moving element can be provided.[0385]
• In a thirteenth aspect of the present invention, in the ninth aspect of the present invention, displacement of the moving element contains displacement rotating in a horizontal direction to a substrate face of the semiconductor substrate. The displacement of the moving element becomes large.[0386]
• In a fourteenth aspect of the present invention, in the eleventh or thirteenth aspect of the present invention, the flexible areas are four flexible areas each shaped like L, the four flexible areas being placed at equal intervals in every direction with the moving element at the center. The lengths of the flexible areas can be increased, so that the displacement of the moving element can be made large.[0387]
• In a fifteenth aspect of the present invention, in the ninth to fourteenth aspect of the present invention, the flexible area is made up of at least two areas having different thermal expansion coefficients and is displaced in response to the difference between the thermal expansion coefficients. As the temperature of the flexible area is changed, the flexible area can be displaced.[0388]
• In a sixteenth aspect of the present invention, in the fifteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of aluminum. As the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between aluminum and silicon.[0389]
• In a seventeenth aspect of the present invention, in the fifteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of nickel. As the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between nickel and silicon.[0390]
• In a eighteenth aspect of the present invention, in the fifteenth aspect of the present invention, at least one of the areas making up the flexible area is made of the same material as the thermal insulation area. Since the flexible area and the thermal insulation area can be formed at the same time, the manufacturing process is simplified and the costs can be reduced.[0391]
• In a nineteenth aspect of the present invention, in the eighteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of polyimide as the area made of the same material as the thermal insulation area. In addition to a similar advantage to that in the invention, as the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between silicon and polyimide, and the heat insulation properties of the flexible area owing to polyimide.[0392]
• In a twentieth aspect of the present invention the invention, in the eighteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of a fluoridated resin as the area made of the same material as the thermal insulation area. In addition to a similar advantage, as the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between silicon and the fluoridated resin, and the heat insulation properties of the flexible area owing to the fluoridated resin.[0393]
• In a twenty-first aspect of the present invention, in the ninth to fourteenth aspect of the present invention, the flexible area is made of a shape memory alloy. As the temperature of the flexible area is changed, the flexible area can be displaced.[0394]
• In a twenty-second aspect of the present invention, in the ninth to twenty-first aspect of the present invention, a thermal insulation area made of a resin for joining the flexible area and the moving element is provided between the flexible area and the moving element. The heat insulation properties between the flexible area and the moving element can be provided and power consumption when the temperature of the flexible area is changed can be more suppressed.[0395]
• In a twenty-third aspect of the present invention, in the twenty-second aspect of the present invention, wherein rigidity of the thermal insulation area provided between the semiconductor substrate and the flexible area is made different from that of the thermal insulation area provided between the flexible area and the moving element. The displacement direction of the moving element can be determined depending on the rigidity difference between the thermal insulation areas.[0396]
• In a twenty-fourth aspect of the present invention, in the ninth to twenty-third aspects of the present invention, the flexible area contains heat means for heating the flexible area. The semiconductor device can be miniaturized.[0397]
• In a twenty-fifth aspect of the present invention, in the ninth to twenty-fifth aspects of the present invention, wiring for supplying power to the heat means for heating the flexible area is formed without the intervention of the thermal insulation area. The heat insulation distance of the wiring can be increased and the heat insulation properties of the flexible area can be enhanced.[0398]
• In a twenty-sixth aspect of the present invention, in the ninth to twenty-fifth aspect of the present invention, the moving element is formed with a concave part. The heat capacity of the moving element is lessened, so that the temperature change of the flexible area can be accelerated.[0399]
• In a twenty-seventh aspect of the present invention, in the ninth to twenty-sixth aspects of the present invention, a round for easing a stress is provided in the proximity of the joint part of the flexible area and the moving element or the semiconductor substrate. The stress applied in the proximity of the joint part when the flexible area is displaced is spread by means of the round, whereby the part can be prevented from being destroyed.[0400]
• In a twenty-eighth aspect of the present invention, in the twenty-seventh aspect of the present invention, the semiconductor substrate is formed with a projection part projecting toward the joint part to the flexible area and the round is formed so that the shape of the round on the substrate face on the semiconductor substrate becomes like R at both ends of the base end part of the projection part. The stress applied to both ends of the base end part of the projection part when the flexible area is displaced is spread by means of the round, whereby the portion can be prevented from being destroyed.[0401]
• In a twenty-ninth aspect of the present invention, in twenty-seventh aspect of the present invention, the semiconductor substrate is etched from the substrate face to make a concave part, the flexible area is formed in a bottom face part of the concave part, and the round is formed so as to become shaped like R on the boundary between the bottom face part and a flank part of the concave part. The stress applied to the boundary between the bottom face part and the flank part of the concave part when the flexible area is displaced is spread by means of the round, whereby the portion can be prevented from being destroyed.[0402]
• According to a thirtieth aspect of the present invention, there is provided a semiconductor microvalve comprising a semiconductor device in any of ninth to twenty-ninth aspects and a fluid element being joined to the semiconductor device and having a flow passage with a flowing fluid quantity changing in response to displacement of the moving element. The semiconductor microvalve which has similar advantages in ninth to twenty-ninth aspect of the present invention as well as can be driven with low power consumption can be provided.[0403]
• In a thirty-first aspect of the present invention, in the thirties of the present invention, the semiconductor device and the fluid element are joined by anodic junction. It is made possible to join the semiconductor device and the fluid element.[0404]
• In a thirty-second aspect of the present invention, in the thirties aspect of the present invention, the semiconductor device and the fluid element are joined by eutectic junction. It is made possible to join the semiconductor device and the fluid element.[0405]
• In a thirty-third aspect of the present invention, in the thirtieth aspect of the present invention, the semiconductor device and the fluid element are joined via a spacer layer. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed in the spacer layer and the stress applied to the flexible area can be suppressed.[0406]
• In a thirty-fourth aspect of the present invention, in the thirty-third aspect of the present invention, the spacer layer is made of polyimide. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed because of elasticity of polyimide and the stress applied to the flexible area can be suppressed.[0407]
• According to a thirty-fifth aspect of the present invention, there is provided a semiconductor microrelay comprising a semiconductor device as the ninth to twenty ninth aspect of the present invention and a fixed element being joined to the semiconductor device and having fixed contacts being placed at positions corresponding to a moving contact provided on the moving element, the fixed contacts being able to come in contact with the moving contact. The semiconductor microrelay which has similar advantages to those in the invention as claimed in claims 9 to 29 as well as can be driven with low power consumption can be provided.[0408]
• In a thirty-sixth aspect of the present invention, in the thirty-fifth aspect of the present invention, the fixed contacts are placed away from each other and come in contact with the moving contact, whereby they are brought into conduction via the moving contact. The semiconductor microrelay wherein the fixed contacts placed away from each other can be brought into conduction can be provided.[0409]
• In a thirty-seventh aspect of the present invention, in the thirty-fifth or thirty-sixth aspect of the present invention, the moving contact and the fixed contacts are gold cobalt. The moving contact and the fixed contacts can be brought into conduction.[0410]
• In a thirty-eighth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined by anodic junction. It is made possible to join the semiconductor device and the fixed element.[0411]
• In a thirty-ninth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined by eutectic junction. It is made possible to join the semiconductor device and the fixed element.[0412]
• In a fortieth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined via a spacer layer. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed in the spacer layer and the stress applied to the flexible area can be suppressed.[0413]
• In a forty-first aspect of the present invention, in the fortieth aspect of the present invention, the spacer layer is made of polyimide. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed because of elasticity of polyimide and the stress applied to the flexible area can be suppressed.[0414]
• According to a forty-second aspect of the present invention, there is provided a manufacturing method of a semiconductor device in the eighteenth aspect of the present invention prepared by a process comprising the steps of:[0415]
• etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;[0416]
• etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;[0417]
• etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0418]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0419]
• applying a coat of the thermal insulation material to the one face of the semiconductor substrate to form one area forming a part of the flexible area.[0420]
• The thermal insulation area and one area forming a part of the flexible area are formed of the same material at the same time, whereby the manufacturing process is simplified and the costs can be reduced.[0421]
• According to a forty-third aspect of the present invention, there is provided a manufacturing method of a semiconductor device area;[0422]
• etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;[0423]
• etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0424]
• forming a wire for applying an electric power to the heating means;[0425]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0426]
• forming a nickel thin film as an area defined in the flexible area on the other face of the semiconductor substrate, whereby the area defined by nickel could be formed in the flexible area.[0427]
• According to a forty-fifth aspect of the present invention there is provided a manufacturing method of a semiconductor device in the first aspect of the present invention prepared by a process comprising the steps of:[0428]
• etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0429]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0430]
• etching and removing the other face of the semiconductor substrate to form the thermal insulation area, whereby the thermal isolation area could be placed between the semiconductor substrate and the flexible area.[0431]
• According to a forty-sixth aspect of the present invention, there is provided a manufacturing method of a semiconductor device in the fifth aspect of the present invention prepared by a process comprising the steps of:[0432]
• etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;[0433]
• forming a reinforce layer in the thermal insulation area;[0434]
• filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and[0435]
• etching and removing the other face of the semiconductor substrate to form the thermal insulation area, whereby the thermal isolation area could be placed between the semiconductor substrate and the flexible area and the reinforce layer could be formed in the thermal insulation area.[0436]

Claims (35)

What is claimed is:

1. A semiconductor device comprising:

a semiconductor substrate;

a flexible area isolated from said semiconductor substrate and displaced in response to temperature change, and

a thermal isolation area placed between said semiconductor substrate and said flexible area and made of a resin for joining said semiconductor substrate and said flexible area.

2. The semiconductor device as claimed inclaim 1, wherein the material of which said thermal isolation area is made has a thermal conductivity coefficient of about 0.4 W/(m ° C.) or less.

3. The semiconductor device as claimed inclaim 1, wherein the material of which said thermal isolation area is made is polyimide.

4. The semiconductor device as claimed inclaim 1, wherein the material of which said thermal isolation area is made is a fluoridated resin.

5. The semiconductor device as claimed inclaim 1, wherein a reinforcement layer made of a harder material than the material of which said thermal isolation area is made is provided on at least one face orthogonal to a thickness direction of said thermal isolation area.

6. The semiconductor device as claimed inclaim 1, wherein the reinforcement layer has a Young's modulus of 9.8×10 N/m²or more.

7. The semiconductor device as claimed inclaim 1, wherein the reinforcement layer is a silicon dioxide thin film.

8. The semiconductor device as claimed inclaim 1, wherein portions of said semiconductor substrate and said flexible area in contact with said thermal isolation area form comb teeth.

9. A semiconductor device comprising:

a semiconductor substrate;

a flexible area isolated from said semiconductor substrate and displaced in response to temperature change;

a thermal isolation area placed between said semiconductor substrate and said flexible area and made of a resin for joining said semiconductor substrate and said flexible area; and

a moving element placed contiguous with the flexible area, said moving element being displaced relative to the semiconductor substrate when temperature of the flexible area changes.

10. The semiconductor device as claimed inclaim 9, wherein the flexible area has a cantilever structure.

11. The semiconductor device as claimed inclaim 9, wherein said moving element is supported by a plurality of flexible areas.

12. The semiconductor device as claimed inclaim 11, wherein the flexible areas are in the shape of a cross with said moving element at the center.

13. The semiconductor device as claimed inclaim 11, wherein displacement of said moving element contains displacement rotating in a horizontal direction to a substrate face of the semiconductor substrate.

14. The semiconductor device as claimed inclaim 11, wherein the flexible areas are four flexible areas each shaped in L, the four flexible areas being placed at equal intervals in every direction with said moving element at the center.

15. The semiconductor device as claimed inclaim 9, wherein the flexible area is made up of at least two areas having different thermal expansion coefficients and is displaced in response to a difference between the thermal expansion coefficients.

16. The semiconductor device as claimed inclaim 15, wherein the flexible area includes an area made of silicon and an area made of aluminum.

17. The semiconductor device as claimed inclaim 15, wherein the flexible area includes an area made of silicon and an area made of nickel.

18. The semiconductor device as claimed inclaim 15, wherein at least one of the areas making up the flexible area is made of the same material as the thermal isolation area.

19. The semiconductor device as claimed inclaim 18, wherein the flexible area includes an area made of silicon and an area made of polyimide as the area made of the same material as the thermal isolation area.

20. The semiconductor device as claimed inclaim 18, wherein the flexible area includes an area made of silicon and an area made of a fluoridated resin as the area made of the same material as the thermal isolation area.

21. The semiconductor device as claimed inclaim 9, wherein the flexible area is made of a shape memory alloy.

22. The semiconductor device as claimed inclaim 9, wherein a thermal insulation area made of a resin for joining the flexible area and said moving element is provided between the flexible area and said moving element.

23. The semiconductor device as claimed inclaim 22, wherein rigidity of the thermal isolation area provided between the semiconductor substrate and the flexible area is made different from that of the thermal isolation area provided between the flexible area and said moving element.

24. The semiconductor device as claimed inclaim 9, wherein the flexible area contains heat means for heating the flexible area.

25. The semiconductor device as claimed inclaim 9 further comprising:

wiring for supplying power to the heat means for heating the flexible area is formed without the intervention of the thermal isolation area.

26. A semiconductor microvalve comprising:

a semiconductor substrate;

a flexible area isolated from said semiconductor substrate and displaced in response to temperature change;

a thermal isolation area placed between said semiconductor substrate and said flexible area and made of a resin for joining said semiconductor substrate and said flexible area; and

a moving element placed contiguous with the flexible area, said moving element being displaced relative to the semiconductor substrate when temperature of the flexible area changes; and

a fluid element being joined to said semiconductor device and having a flow passage with a flowing fluid quantity changing in response to displacement of the moving element.

27. The semiconductor microvalve as claimed inclaim 26, wherein said semiconductor device and said fluid element are joined via a spacer layer.

28. A semiconductor microrelay comprising:

a semiconductor substrate;

a flexible area isolated from said semiconductor substrate and displaced in response to temperature change;

a thermal isolation area placed between said semiconductor substrate and said flexible area and made of a resin for joining said semiconductor substrate and said flexible area; and

a moving element placed contiguous with the flexible area, said moving element being displaced relative to the semiconductor substrate when temperature of the flexible area changes; and

a fixed element joined to said semiconductor device and having fixed contacts being placed at positions corresponding to a moving contact provided on the moving element, the fixed contacts being able to come in contact with the moving contact.

29. The semiconductor microrelay as claimed inclaim 28, wherein the fixed contacts are placed away from each other and come in contact with the moving contact, whereby they are brought into conduction via the moving contact.

30. The semiconductor microrelay as claimed inclaim 28, wherein said semiconductor device and said fixed element are joined via a spacer layer.

31. A manufacturing method of a semiconductor device as claimed inclaim 18 prepared by a process comprising the steps of:

etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;

etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;

etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal isolation area placed between the semiconductor substrate and the flexible area;

filling the portion which becomes the thermal area with a thermal insulation material to form the thermal insulation area; and

applying a coat of the thermal insulation material to the one face of the semiconductor substrate to form one area forming a part of the flexible area.

32. A manufacturing method of a semiconductor device as claimed inclaim 16 prepared by a process comprising the steps of:

etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;

etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;

etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal isolation area placed between the semiconductor substrate and the flexible area;

forming an aluminum thin film as an area defined in the flexible area on the other face of the semiconductor substrate and a wire for applying an electric power to the heating means;

filling the portion which becomes the thermal area with a thermal insulation material to form the thermal area.

33. A manufacturing method of a semiconductor device as claimed inclaim 17 prepared by a process comprising the steps of:

etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;

etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;

etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal isolation area placed between the semiconductor substrate and the flexible area;

forming a wire for applying an electric power to the heating means;

filling the portion which becomes the thermal area with a thermal insulation material to form the thermal area; and

forming a nickel thin film as an area defined in the flexible area on the other face of the semiconductor substrate.

34. A manufacturing method of a semiconductor device as claimed inclaim 1 prepared by a process comprising the steps of:

etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal isolation area placed between the semiconductor substrate and the flexible area;

filling the portion which becomes the thermal isolation area with a thermal insulation material to form the thermal isolation area; and

etching and removing the other face of the semiconductor substrate to form the thermal insulation area.

35. A manufacturing method of a semiconductor device as claimed inclaim 5 prepared by a process comprising the steps of:

etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;

forming a reinforce layer in the thermal insulation area;

filling the portion which becomes the thermal isolation area with a thermal insulation material to form the thermal isolation area; and

etching and removing the other face of the semiconductor substrate to form the thermal isolation area.

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